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Mateusz Gładysz

Pathway read-through · Eccrine and poroid tumours

Eccrine and poroid tumours in the digital and acral nodule differential

Mateusz Gładysz · MD · FEBOPRAS · FEBHS

A clinician read through for hand and plastic surgery

Clinical content verified References checked 6 questions Version 1.0

A persistent acral nodule can be a benign adnexal tumour, a common hand lesion, or a malignancy whose surface appearance understates its extent. The useful sequence is to establish the anatomical compartment, obtain a representative specimen without compromising subsequent treatment, secure a morphological diagnosis, and then plan definitive treatment around the tumour actually found. “Eccrine” is a differentiation label, not a clinical diagnosis or a guarantee of benign behaviour.

This article concerns general clinician education. It contains no patient vignette and does not replace specialist dermatopathology review, a melanoma or skin-cancer pathway, or multidisciplinary decision-making. Evidence for rare adnexal malignancies is dominated by retrospective series and selected published cases; recommendations borrowed from melanoma or cutaneous squamous-cell carcinoma are identified as such.

Learning objectives

After this read-through, the clinician should be able to:

  • distinguish poroid architecture from evidence of malignant behaviour;
  • choose a biopsy that respects the compartment, melanoma risk and need for depth;
  • recognise when immunohistochemistry or molecular testing helps, and when it cannot decide;
  • separate evidence-supported treatment aims from uncertain margin, nodal and systemic strategies.
Applied questionsClinic refresher
Applied learning

These questions and two examples are entirely fictional teaching constructions. They contain no real patient, personal identifiers or clinical record. Their purpose is to practise the reasoning steps in the read-through, not to prescribe care for an individual.

For each question, select an answer and record confidence: guess, fairly sure or certain.

Confidence feedback for every answer: Correct and certain means retain the rule but check its limits. Correct with lower confidence means revisit the explanation and source. Incorrect with lower confidence identifies a learning gap. Incorrect and certain identifies a misconception worth correcting before applying it. This is a learning aid, not a competence score; a correct answer does not establish a diagnosis.

1What does eccrine mean here

Normal eccrine units comprise a secretory coil and a duct that reaches the epidermal surface. Traditional adnexal classification names tumours by the structures they resemble. A poroid tumour shows small cuboidal poroid cells, larger cuticular cells and ductal differentiation. However, the historical phrase “eccrine poroma” does not establish an exclusively eccrine cell of origin. Apocrine features and overlapping lines of differentiation occur, and molecular findings increasingly organise tumours by related biology rather than a simple eccrine–apocrine division. 123

Basics

Four familiar benign patterns explain much of the terminology:

  • Poroma: a predominantly epidermis-connected proliferation extending into the dermis.
  • Hidroacanthoma simplex: an intraepidermal poroid proliferation.
  • Dermal duct tumour: a predominantly dermal poroid proliferation.
  • Poroid hidradenoma: a dermal, often solid-and-cystic tumour with hidradenoma-like architecture.

These are architectural patterns; more than one may coexist. The word “hidradenoma” alone is broader than poroid hidradenoma and should not be treated as a synonym. Architecture helps name the lesion, but cytological and growth-pattern assessment determine whether a malignant component is present. 2

Porocarcinoma is a malignant poroid adnexal neoplasm. It can occur with a residual benign poroma or without an identified precursor. Neither a longstanding history nor a small benign-looking surface rules it out. Conversely, the possibility of malignant transformation does not justify telling every person with a poroma that cancer is likely: a reliable population-level transformation probability is not established by selected tumour series. 42

2Start with the compartment and the clinical problem

The first examination should distinguish an epidermal or dermal lesion from a deeper mass related to tendon sheath, joint, nerve or bone. Record the precise site, size, surface, mobility, depth, nail-unit involvement and relation to function. Change in growth, bleeding, ulceration, recurrence after treatment, fixation, sensory symptoms or regional nodes should alter the threshold for tissue diagnosis. None is specific for an eccrine malignancy. 564

A practical differential follows the anatomy. Descriptive clinical series support the listed tumour spectrum; the anatomical grouping is a clinical synthesis. 56782836

PresentationDiagnoses to keep in viewWhat prevents premature closure
Superficial pink, red, keratotic or verrucous nodulePoroma, pyogenic granuloma, wart, acquired digital fibrokeratoma, SCC or keratoacanthoma, amelanotic melanomaBleeding, vascularity and keratin are shared features; a clinical label needs histological confirmation when the course is atypical.
Pigmented acral or periungual lesionMelanocytic lesion or melanoma, pigmented poroma, pigmented keratinocytic lesionPigmentation does not establish melanocytic origin, and lack of pigment does not exclude melanoma.
Deep, slow-growing digital noduleTenosynovial giant-cell tumour, ganglion or mucous cyst, epidermoid cyst, nerve-sheath lesion, digital papillary adenocarcinomaEstablish the tissue compartment; a well-circumscribed mass can still require oncological planning.
Painful subungual or fingertip lesionGlomus tumour and other painful benign tumours, infection or inflammatory disease, SCC, melanoma or digital papillary adenocarcinomaPain and a characteristic site narrow the differential but do not replace appropriate imaging or biopsy.
Persistent nail dystrophy, periungual growth or nail-bed lesionSCC, melanoma, benign nail tumours and inflammatory or infectious diseaseRepeated treatment of an assumed benign diagnosis should not continue when the clinical course and tissue diagnosis disagree.

This anatomical framework is a clinical synthesis, not a validated diagnostic score or a prevalence ranking. On a digit, anatomy and the consequences of an incorrectly placed biopsy matter as much as the apparent size of the lesion. Plain radiographs may help when a subungual or distal-digit lesion raises concern about bone involvement. Ultrasound or MRI may help define a deep mass and its relation to critical structures; they do not establish the histological identity of a superficial poroid tumour. A suspected deep soft-tissue malignancy calls for specialist assessment before an unplanned excision. This imaging and referral approach is anatomy-led clinical reasoning, rather than a poroma-specific tested algorithm.

What dermoscopy contributes

A multicentre case-control study of 113 poromas and 106 controls evaluated five features: white interlacing perivascular areas, yellow structureless areas, milky-red globules, poorly visualised vessels, and branched vessels with rounded endings. Presence of any one feature gave 62.8% sensitivity and 82.0% specificity; the last feature did not have an independently significant adjusted association. Most poromas in this selected study were non-acral, so these results do not describe an unselected digital-nodule clinic. Absence of the proposed features cannot exclude poroma, and their presence cannot establish benignity or safely exclude melanoma. 9

Dermoscopy is therefore useful for describing heterogeneity and selecting an appropriate biopsy target. It is not a substitute for an adequately sampled specimen, and there is no validated dermoscopic route from “looks like poroma” to “malignancy excluded.” 9

Question 1 · A reassuring surface

A superficial acral nodule has several vascular features reported in poroma. Which conclusion is justified?
□ Guess · □ Fairly sure · □ Certain
✗ (a)

A poroma-like vascular pattern cannot establish benign behaviour.

✗ (b)

Melanoma can be amelanotic; absent pigment does not exclude it.

✓ (c)

In the published case-control study, the proposed rule had 62.8% sensitivity and 82.0% specificity. It was not a digit-specific malignant-lesion exclusion rule. Confidence in a visual pattern should not exceed the test’s demonstrated role.

Confidence calibration

The evidence supports confidence in the need for clinicopathological correlation, not certainty about a visually inferred tumour. The published rule uses any one of five features and came from a mostly non-acral sample.

✗ (d)

The rule’s limited sensitivity means missing features cannot exclude a poroid tumour.

Question 1 sources: 9

3Choose the biopsy around the diagnosis that would change the operation

The correct question is not “punch or excision?” in isolation. It is whether the specimen will preserve the architecture and depth needed to distinguish benign from malignant disease and to plan the next operation. Communicate the site, growth history, previous procedures, relevant differential and any discordance between surface appearance and deeper findings to the pathologist. Orient a specimen when margin localisation could change subsequent surgery. 101112

When removal is intended to resolve an uncertain diagnosis, preserve and submit tissue for histology even if the provisional label is pyogenic granuloma, wart or fibrokeratoma. This diagnostic principle does not imply that every clinically typical wart requires biopsy.

If melanoma is a realistic possibility, use melanoma biopsy principles. ESMO recommends complete, full-thickness excision with a minimal margin of uninvolved skin when feasible. For larger lesions where complete excision would require reconstructive surgery, ESMO permits an appropriately planned biopsy. AAD guidance describes a narrow complete biopsy, usually with 1–3 mm clinical margins, and recognises elliptical excision, a punch that encompasses the entire lesion, or sufficiently deep saucerisation as ways of obtaining it. A complete deep saucerisation is different from a superficial shave that transects a suspected invasive tumour. 1310

Partial biopsy may be necessary for a large or anatomically difficult acral lesion, but the sampling limitation must remain visible in subsequent decisions. In a retrospective series of 2,304 melanomas, upstaging after definitive excision was more common after partial sampling than after excisional biopsy; acral lentiginous melanomas were particularly vulnerable to understaging. Technique selection was not random, and the reported shave group cannot be assumed to represent either uniformly superficial shaves or complete deep saucerisations. The findings support careful planning, clinicopathological correlation and further diagnostic sampling when microstaging remains uncertain, not a blanket prohibition of partial biopsy. 14

The nail unit deserves separate attention. Identify whether the target is matrix, bed, fold or hyponychium; a matrix-origin pigment band and a true nail-bed mass are different sampling problems. This is an anatomical planning principle, not a single technique for all nail lesions.

Dika and colleagues studied 86 nail specimens obtained for suspected nail melanoma or a melanocytic/pigmentary differential, not an unselected population of nail nodules or amelanotic masses. Thirteen of 23 punch specimens were nondiagnostic: the failures were nail-bed samples where matrix-origin pigmentation required assessment. Correctly targeted matrix punches were diagnostic. All 60 longitudinal and all three tangential specimens were diagnostic, although the tangential specimens limited assessment of tumour extension and subsequent Breslow thickness. Technique selection was not randomised. This supports the right anatomical target and adequate architecture; it does not make bed sampling wrong for a lesion genuinely arising in the bed. 15

For a suspected deeply infiltrative adnexal tumour, a superficial specimen can miss the diagnostic growth pattern. The microcystic adnexal carcinoma guideline specifically recommends a deep biopsy including subcutis. For a heterogeneous poroid lesion, a limited bland sample may likewise fail to explain the clinically concerning component. Request deeper levels, expert review or further tissue when findings do not fit; do not let the reassuring word in a small specimen end the inquiry. 124

Biopsy planning and reconstruction planning are connected. A definitive flap or major tissue rearrangement can make further margin-directed surgery more difficult. Where malignant diagnosis or clearance remains unresolved, consider a staged approach appropriate to the anatomy and tumour. The principle of confirming negative margins before significant tissue rearrangement is explicit in high-risk cSCC guidance; its use for rare adnexal tumours is a planning extrapolation, not evidence that a flap biologically spreads malignancy. 11

Question 2 · A constrained biopsy

A larger cutaneous lesion on an anatomically constrained acral site has melanoma in its differential. Complete removal would require reconstructive surgery. Which principle is most defensible?
□ Guess · □ Fairly sure · □ Certain
✗ (a)

A diagnostic biopsy and definitive oncological excision are different steps; no universal porocarcinoma margin is established.

✓ (b)

Complete full-thickness narrow-margin biopsy is preferred when feasible, but ESMO allows biopsy for larger lesions where complete removal requires reconstruction. AAD distinguishes complete punch excision and deep saucerisation from partial or superficial sampling. Subsequent decisions must acknowledge what the specimen cannot measure.

Confidence calibration

ESMO’s reconstruction exception is phrased for larger lesions. AAD separately permits selected partial biopsies at acral or difficult sites. Neither removes the need to document sampling limitations.

✗ (c)

A superficial shave may transect a lesion; a sufficiently deep complete saucerisation is designed to preserve relevant depth.

✗ (d)

A punch can encompass an entire small lesion or sample only part of a larger one.

Question 2 sources: 131014

Question 3 · A nondiagnostic nail sample

A nail-bed punch does not explain longitudinal melanonychia thought to originate in the matrix. What is the central problem?
□ Guess · □ Fairly sure · □ Certain
✗ (a)

Correctly targeted matrix punches were diagnostic in this series.

✗ (b)

Nondiagnostic tissue establishes neither benignity nor malignancy.

✓ (c)

In the cited melanocytic/pigmentary nail-biopsy series, nondiagnostic punches were bed samples where matrix assessment was needed; properly targeted matrix punches were diagnostic. The study supports correct targeting and adequate architecture, not a universal ranking of instruments independent of anatomy.

Confidence calibration

Dika’s cohort concerned suspected nail melanoma or a melanocytic/pigmentary differential. Do not extend its findings into a rule that bed biopsy is wrong for a true nail-bed mass, or that one technique suits every nail nodule.

✗ (d)

A bed sample cannot reliably exclude pathology in an unsampled matrix.

Question 3 sources: 15

Fictional worked example 1 · The sample does not explain the lesion

Teaching setup: A small superficial acral nodule is clinically heterogeneous. A limited sample from one smooth area is reported as a benign poroid tumour, but a separate firm ulcerated component was not sampled. No age, sex, laterality, measurement or personal history is implied.

Step 1 — Define the unresolved question. The pathology explains the tissue received. It has not necessarily explained the whole lesion. The issue is representativeness, not a presumption that the initial pathologist made an error.

Step 2 — Reconcile anatomy and specimen. Review the clinical photograph or site description, original slides and specimen depth with pathology. Identify whether the unsampled component or deeper extent could alter classification.

Step 3 — Obtain the missing information. Arrange further appropriate tissue or complete diagnostic removal according to anatomy and the malignant alternatives, keeping melanoma principles in view where relevant. Preserve and submit the diagnostic tissue. Avoid a destructive treatment that would remove the opportunity to assess the unresolved component.

Step 4 — Defer the final operative label. Definitive margin and reconstruction decisions follow the final classification and the chosen method of margin assessment.

Model summary: “The benign partial specimen does not explain the heterogeneous lesion. Reconcile the specimen with the examination and obtain representative tissue before selecting definitive treatment.”

What changes the answer: A complete, adequately sampled specimen with concordant benign morphology may resolve the uncertainty and permit routine local management. 2 4 10 11

4Read the pathology as a set of answered and unanswered questions

Benign poroma and porocarcinoma

A benign poroid tumour is typically composed of relatively uniform poroid and cuticular cells with ductal lumina. Porocarcinoma requires assessment of the whole morphological pattern: cytological atypia, mitotic activity, necrosis and an invasive or otherwise malignant growth pattern, with ductal differentiation supporting the poroid diagnosis. An epidermal connection or a benign poroma component may help, but neither is mandatory. Squamous differentiation can obscure the distinction from SCC. 42

The key differential is not solved by one positive immunostain. EMA and CEA can highlight ductal structures, but this does not independently establish porocarcinoma. 4 CEA and cytokeratin expression can overlap with SCC, and neither a ductal stain nor a shared molecular alteration alone establishes primary cutaneous origin. 1619 A morphology-led panel should address the specific alternatives, including SCC, other adnexal carcinomas, melanoma when relevant, and a metastasis when the pattern or clinical context raises it. 16171819

What molecular findings add

Recurrent YAP1-related fusions, including YAP1–MAML2 and YAP1–NUTM1, helped establish a molecular relationship among many poromas and porocarcinomas. YAP1 immunohistochemical patterns and NUT staining can assist selected difficult diagnoses, with molecular confirmation where appropriate. They are ancillary tests, not universal screening results and not standalone tests of malignancy. A more recent cross-institutional molecular study demonstrated substantial heterogeneity among porocarcinomas. 20 Earlier discovery and diagnostic cohorts also contained fusion-negative or surrogate-negative carcinomas, so absence of a YAP1-related finding cannot exclude the diagnosis. 317

Two recent findings sharpen this caution. YAP1/PAK-family rearrangements have also been reported in follicular tumours, limiting a simple claim of absolute poroid specificity. A distinct NUT-associated adnexal carcinoma has been described: NUT positivity is therefore not sufficient to rename a tumour porocarcinoma. The practical question for the pathologist is whether a molecular result fits the morphology and differential, rather than whether it supplies an automatic label. 2122

Ki-67 also needs context. A recent comparison of 48 poromas and 21 porocarcinomas did not support it as a decisive discriminator. Its small tissue-microarray cores and analytic limitations prevent the opposite claim that Ki-67 is never informative, but a fixed universal cutoff should not overrule morphology. 23

The information needed before definitive treatment

For an invasive porocarcinoma, request a report that makes the following interpretable: diagnostic certainty and differential; tumour dimensions where assessable; thickness or depth with the measurement method; invasive growth pattern; mitotic activity with units and field area where possible; lymphovascular and perineural invasion; any in-situ or associated benign component; and peripheral and deep margin status with distances and orientation. Note when a partial specimen cannot answer a question. This is a practical clinical checklist, not a claim that a universally validated porocarcinoma reporting dataset exists. 424

In Robson and colleagues’ retrospective 69-case study, greater depth, high mitotic activity and lymphovascular invasion were associated with death; an infiltrative advancing margin was associated with local recurrence. These estimates were imprecise and do not establish validated treatment thresholds. Report mitotic activity with a clear denominator or measured area rather than treating a historical high-power-field count as a portable staging rule. 4

That mixed in-situ and invasive series had follow-up for 54 patients: nine had local recurrence and ten developed nodal metastasis. Those counts describe that selected followed cohort. They are not universal risks for every newly diagnosed lesion, and neither outcome is interchangeable with disease-specific mortality. 4

A contemporary SEER analysis of 953 cases reported five-year cancer-specific survival of 97.6% for localised, 76.6% for regional and 47.6% for distant disease. The distant group contained only 12 patients, and registry coding, missing pathological information and cause-of-death classification limit interpretation. These stage-dependent estimates illustrate why a single historical “metastatic mortality” percentage is misleading; they do not supply an individual prognosis or information on local recurrence. 25

Question 4 · A molecular shortcut

An adnexal tumour is NUT-positive. Which interpretation is appropriate?
□ Guess · □ Fairly sure · □ Certain
✗ (a)

The poroid family and distinct NUT-associated adnexal tumours can share a positive stain.

✗ (b)

Benign poroid tumours can harbour relevant fusions; small series have differing positivity patterns.

✓ (c)

YAP1–NUTM1 occurs in the poroid family, including benign tumours; distinct primary cutaneous NUT adnexal carcinomas have different fusion partners and molecular features. A positive stain assists a differential rather than replacing it.

Confidence calibration

Be confident that morphology and molecular context must agree; avoid certainty based on one marker. The independent validation study reinforces histomorphological correlation.

✗ (d)

A classification clue does not determine an established porocarcinoma treatment regimen.

Question 4 sources: 3172218

5Treat the diagnosis and extent rather than a memorised margin

Benign disease

When an adequately assessed lesion is a benign poroma, complete local removal is generally sufficient when treatment is needed. The important caveat is diagnostic adequacy: destructive treatment provides no intact specimen for resolving an uncertain or changing lesion. If a lesion recurs or changes after an apparently benign diagnosis, reassess the original pathology and the new clinical findings rather than assuming the original label remains complete. 2

Localised porocarcinoma

The consistent treatment objective is complete histological clearance. Both conventional excision and margin-controlled approaches, including Mohs or staged excision, are reported. Margin-controlled surgery is attractive where tissue preservation matters or the tumour is ill-defined, recurrent or infiltrative, but published series do not establish a universally superior technique for every porocarcinoma. 2627

There is no prospectively validated clinical margin width that can simply be assigned to every porocarcinoma. Reported margins differ with lesion size, growth pattern, site and study design. On a digit, an arbitrary centimetre rule may sacrifice function without answering the more important questions of peripheral and deep clearance. Choose the method with the relevant surgical and dermatopathology expertise; establish how margins will be assessed and when definitive reconstruction is appropriate. 2627

Amputation is not an automatic consequence of an adnexal malignancy diagnosis. Equally, a tissue-sparing operation is not adequate merely because function is preserved. The decision depends on the particular tumour, confirmed extent, achievable clearance and functional result. Deep involvement, bone or tendon involvement, recurrent disease and uncertainty about the diagnosis warrant multidisciplinary planning rather than a generic poroma pathway. 282927

Nodes and imaging

Examine the relevant nodal basin and investigate clinically suspicious nodes through a cancer pathway. Imaging is most useful when it addresses a defined question: local deep extent, a suspicious basin, or possible distant disease. Evidence does not establish routine whole-body staging or sentinel lymph-node biopsy for every small clinically node-negative porocarcinoma. 2427

A 2026 national-database study of 1,351 patients proposed considering sentinel-node biopsy for tumours larger than 17 mm or with lymphovascular invasion. This was a retrospective association and author recommendation, not prospective validation of a threshold or proof that sentinel-node biopsy improves survival. Small sentinel-node series can inform an MDT discussion, but they do not settle patient selection, benefit or optimal subsequent management. 24

Do not import melanoma or cSCC nodal thresholds without naming the extrapolation. A positive node, local recurrence and distant metastasis represent different clinical problems and need tumour-specific review. Therapeutic nodal treatment is distinct from performing an elective staging procedure in a clinically node-negative patient. 24

Radiotherapy and systemic treatment

Radiotherapy has been used for selected unresectable tumours and as an adjunct in high-risk or incompletely controlled disease, but comparative evidence defining its indications in porocarcinoma is limited. Decisions should state the intended benefit and the uncertainty rather than presenting it as routine after every high-risk pathological feature. A dedicated postoperative review found only 14 case reports. 30

For unresectable or metastatic disease, no disease-specific systemic regimen is established by randomised porocarcinoma trials. Responses to chemotherapy, EGFR-directed treatment and PD-1 blockade have been described, largely in case reports and small reports. A 2026 phase-1 study across mixed solid tumours also included a confirmed partial response in one porocarcinoma after an anti-NKG2A lead-in followed by anti-PD-1 treatment. This is a signal from an early-phase, mixed-population study, not a porocarcinoma response rate or standard of care. 31322733

Expert oncological review, an appropriate clinical trial and molecular testing when it could inform a realistic treatment option are reasonable considerations. Availability, licensing and funding should be checked locally at the time treatment is considered. 31322733

Question 5 · A registry threshold

A clinically node-negative porocarcinoma has a feature associated with nodal disease in retrospective research. What does that evidence establish?
□ Guess · □ Fairly sure · □ Certain
✗ (a)

A retrospective association does not establish a mandatory intervention or survival benefit.

✓ (b)

The recent national-database analysis proposed size and lymphovascular-invasion criteria for consideration. It was not a prospective intervention study and did not establish survival benefit from SLNB. Association, staging yield and treatment benefit are separate questions.

Confidence calibration

Separate a risk association, a staging test’s yield, and proof that performing the test improves outcomes.

✗ (c)

Normal clinical nodes do not exclude occult nodal disease.

✗ (d)

Melanoma thresholds were developed for a different disease and cannot be imported unchanged.

Question 5 sources: 24

Fictional worked example 2 · Clearance and nodes are separate decisions

Teaching setup: A specialist review confirms a primary porocarcinoma on an acral site; the lesion is clinically node-negative. The report describes an infiltrative component and lymphovascular invasion. These features are chosen solely to illustrate evidence interpretation and are unrelated to any real case.

Step 1 — Check the report’s limits. Confirm diagnostic certainty, specimen completeness, depth, growth pattern, mitotic units and margin status. Do not translate a historical association into an automatic stage; Robson associated infiltrative borders with local recurrence.

Step 2 — Set the local objective. Plan complete histological clearance. Consider the tumour’s extent, function and available margin-control expertise rather than selecting an unsupported universal centimetre margin.

Step 3 — Ask a separate nodal question. Lymphovascular invasion makes discussion of nodal staging reasonable. The available retrospective evidence supports consideration, not a mandate or a proven survival benefit from SLNB. Select investigations that answer an explicit clinical question.

Step 4 — Coordinate reconstruction and follow-up. Agree how and when clearance will be established, when definitive reconstruction is suitable, and who owns local and nodal review. Record where decisions rely on extrapolation.

Model summary: “Secure local clearance with a method suited to anatomy and growth pattern. Discuss nodal staging separately, documenting the adverse feature and the limits of the SLNB evidence.”

What changes the answer: A clinically suspicious node requires diagnostic assessment of possible established nodal disease; that is a different problem from elective sentinel-node staging of a clinically normal basin. 4 26 27 24

6Wider adnexal diagnoses that change the hand surgeon’s plan

Digital papillary adenocarcinoma deserves particular attention in a digital nodule. It may present as an apparently indolent dermal or subcutaneous mass. In a 31-case clinicopathological series with follow-up available for 23, histological features did not reliably predict behaviour, and metastasis could occur many years later. A myoepithelial layer is not proof that the lesion is benign. Older “adenoma” versus “adenocarcinoma” language should not create false reassurance. Definitive clearance, assessment by an experienced team and a long-term surveillance plan matter; the evidence does not justify converting selected-series outcomes into a precise individual prognosis. 28

HPV42 has a strong molecular association with digital papillary adenocarcinoma and can assist a difficult differential using an appropriate assay; p16 alone does not establish HPV42 status; an appropriate HPV42 assay must be interpreted with morphology. 3435 A 21-patient institutional series found positive SLNB in three of the 18 patients who underwent it, with an association with subsequent recurrence. This supports discussion of staging, not proof of a survival benefit from SLNB or completion dissection. Prompt definitive clearance remains the aim. Pooled observational literature has not established that amputation is universally superior to margin-negative digit-preserving excision. 34353629

Microcystic adnexal carcinoma is much more characteristic of the head and neck than the digit, but it illustrates a crucial diagnostic trap: bland superficial morphology can coexist with deep infiltration and perineural growth. A sufficiently deep specimen and margin-controlled treatment are central recommendations in its clinical practice guideline. Its behaviour and management should not be inferred from the porocarcinoma literature. 12

Hidradenoma and hidradenocarcinoma, spiradenoma and spiradenocarcinoma, and other adnexal carcinomas require their own morphological classification. A tender lesion is not necessarily benign, and a generic report of “sweat-gland tumour” may be insufficient for definitive planning. For hidradenocarcinoma, infiltrative growth, necrosis, atypia and proliferative activity need integrated assessment. 37 CRTC1::MAML2 can occur in both benign and malignant hidradenoma-family tumours. The fusion partner matters: MAML2 break-apart positivity alone does not distinguish that family from a YAP1::MAML2-associated poroid tumour, and neither result decides benignity. 383 Spiradenoma-family tumours can show CYLD or ALPK1 alterations, but malignant transformation still requires morphology. 39 When the label remains broad, ask what has been excluded, whether the specimen is representative and whether specialist review would resolve the uncertainty.

The same discipline applies to non-adnexal diagnoses. Nail-unit SCC and melanoma, conventional cutaneous SCC, and a deep soft-tissue sarcoma are not variants of the eccrine problem. Once the diagnosis changes, the staging and treatment pathway must change with it. 10115

Question 6 · A bland distal-digit adenocarcinoma

A specialist report identifies digital papillary adenocarcinoma with relatively bland cells and a retained myoepithelial layer. Which response is appropriate?
□ Guess · □ Fairly sure · □ Certain
✗ (a)

A retained myoepithelial layer does not establish benignity in digital papillary adenocarcinoma.

✗ (b)

Digital papillary adenocarcinoma is a distinct malignant entity, not a poroma variant.

✓ (c)

Bland cytology and myoepithelial retention do not establish benignity in this tumour. Late metastases are documented. Digit preservation versus amputation depends on extent and achievable clearance; observational evidence does not make either procedure universally correct.

Confidence calibration

Margin-negative digit preservation may be feasible, but observational comparisons do not prove equivalence with amputation in every setting. Choose neither universally from these data.

✗ (d)

The tumour’s name does not dictate the operation; extent and achievable clearance matter.

Question 6 sources: 2829

7A clinic sequence that keeps uncertainty visible

  1. Locate the lesion. Skin, nail matrix or bed, subcutis, tendon sheath, nerve and bone imply different differentials and biopsy hazards.
  2. Name the dangerous alternative. Decide whether melanoma, SCC, a malignant adnexal tumour or a deep soft-tissue malignancy would change the biopsy or referral plan.
  3. Obtain the right tissue. Preserve depth and architecture; target the relevant component; communicate the differential and any reconstruction constraint.
  4. Reconcile the report with the examination. A benign partial sample is insufficient when it does not explain growth, ulceration, depth or recurrence.
  5. Secure classification and clearance. Ask for specialist review when needed, then choose margin assessment and reconstruction timing for the actual tumour.
  6. Separate local, nodal and systemic decisions. Record what is known, what is extrapolated, and which question requires MDT discussion.
  7. Make follow-up explicit. Provide a responsible service, a review plan and triggers for reassessment. There is no universally validated porocarcinoma follow-up schedule; intensity should reflect the diagnosis, extent, risk features and treatment. 4122428

Clinic refresher

Core sequence: locate the lesion → preserve diagnostic architecture and depth → reconcile pathology with the clinical finding → plan clearance and reconstruction → separate local, nodal and systemic decisions.

Before biopsy

  • Establish skin versus nail matrix/bed versus a deeper mass. Record size, growth, ulceration/bleeding, pain, fixation, prior treatment, nail changes and functional or sensory findings.
  • Keep poroma, SCC, amelanotic melanoma, pyogenic granuloma and wart in view. For a deeper or painful distal-digit nodule, include digital papillary adenocarcinoma alongside benign hand lesions.
  • Dermoscopy helps describe and target a lesion. It cannot certify a poroma as benign; the published any-one-of-five-feature rule had 62.8% sensitivity in a selected, mostly non-acral population. 9

Plain radiographs can address suspected bone involvement; ultrasound or MRI may localise soft-tissue disease. Select imaging for the anatomical question.

Obtain tissue that answers the important question

  • If melanoma is plausible, aim for a complete full-thickness narrow-margin diagnostic specimen where feasible. ESMO allows planned biopsy of larger lesions requiring reconstruction; AAD permits selected partial biopsy at constrained sites. A complete deep saucerisation is different from a superficial transecting shave. 13 10
  • Target the correct nail structure. In a melanocytic/pigmentary nail series, nondiagnostic bed punches missed suspected matrix-origin pigmentation. A true bed mass has a different target. 15
  • Suspected infiltrative adnexal disease needs adequate depth. Microcystic adnexal carcinoma guidance specifically calls for a biopsy including subcutis. 12
  • A benign partial biopsy that does not explain the lesion needs review or further tissue. Plan substantial reconstruction around the diagnosis and the means of confirming clearance. 11

Read the report critically

  • “Eccrine” describes differentiation. Poroma, hidroacanthoma simplex, dermal duct tumour and poroid hidradenoma are architectural patterns, not four grades.
  • Porocarcinoma is a morphological diagnosis integrating poroid/ductal differentiation and malignant growth or cytology. EMA/CEA, YAP1-related findings and NUT can assist; none alone proves malignancy. 4 16 3 22
  • Ask for depth, growth pattern, mitoses with denominator, lymphovascular/perineural invasion and oriented margin status. Identify what a partial sample cannot assess.
  • Historical depth, mitotic and lymphovascular-invasion associations concerned death; infiltrative borders were associated with local recurrence. These are not validated automatic treatment thresholds. 4

After malignant diagnosis

  • Seek specialist dermatopathology and MDT input. The local objective is complete histological clearance; no universal porocarcinoma excision margin is prospectively validated. Margin control may be useful where tissue preservation matters. 26 27
  • Examine nodes and investigate suspicious findings. Routine SLNB for every porocarcinoma is unproven; size/LVI proposals from retrospective registries remain discussion points. 24
  • Digital papillary adenocarcinoma needs its own plan. Bland histology or retained myoepithelial cells do not establish benignity, and late metastasis has been described. 28
  • Systemic treatment evidence is limited; promising case responses and a single porocarcinoma response within a mixed-tumour phase-1 trial do not establish a standard regimen. 31 32 33

Avoid: wrong-site nail sampling; unexplained clinicopathological discordance; one-stain diagnosis; arbitrary margins; equating local recurrence, nodal metastasis and mortality; definitive tissue rearrangement before the clearance strategy is settled.

General educational aid. Use the full read-through for the evidence, limitations and numbered references; this is not a patient-specific management protocol.

Learning summary

Answer key

Frequently asked questions

Is a poroma always an acral tumour

No. Acral occurrence is a useful association, but poromas occur at other sites. Site alone cannot confirm or exclude the diagnosis. 29

Can a benign-looking poroma be treated without histology

When the diagnosis is uncertain, the lesion is changing, or malignancy would change treatment, tissue diagnosis is the safer basis for planning. Destruction removes the opportunity to evaluate the full lesion. 211

Does a positive NUT or YAP1-associated result prove porocarcinoma

No. These findings can support classification in the right morphological setting. They do not independently establish malignancy, and recently described overlapping or distinct tumours limit absolute specificity. 32122

Does porocarcinoma automatically require a sentinel node biopsy

No established evidence-based universal rule does. Retrospective studies identify factors associated with nodal disease, but the benefit and selection criteria for elective sentinel-node biopsy remain uncertain. 24

Is there a standard wide excision margin

No universally validated margin applies to all porocarcinomas. The objective is complete histological clearance, using a method suited to tumour extent, architecture, anatomy and available expertise. 2627

Which mistakes are most avoidable

Calling an unexplained lesion a wart or pyogenic granuloma indefinitely; taking tissue from the wrong nail-unit structure; accepting a superficial or partial specimen that does not answer the clinical question; treating a ductal stain as a diagnosis; reconstructing before the clearance plan is settled; and quoting selected-series recurrence or metastasis rates as an individual prognosis. 1517114

This targeted literature review is not an exhaustive systematic review. Primary studies and disease-specific guidelines are prioritised; selected reviews support classification and areas without a guideline. Several rare-tumour claims were checked only against abstracts; full text may be available but was not reviewed in every case.

References

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