Diagnosis & biopsy

Biopsy technique by suspected tumour

Suspected melanoma

The UK standard is a narrow-margin (2 mm) excisional biopsy down to and including subcutis — the entire lesion plus a small surrounding cuff of normal skin. This allows accurate Breslow thickness measurement (from top of granular layer to deepest tumour cell), assessment of ulceration, mitotic count, and lymphovascular / perineural invasion.

• Never shave a lesion clinically suspicious for melanoma — shave biopsy transects the deep margin and renders Breslow measurement inaccurate, potentially under-staging the tumour.
• Punch / incisional biopsy is reserved for large lesions (e.g. extensive lentigo maligna of the cheek) or functionally critical sites (eyelid, distal digit) where total excisional biopsy is impractical — and only after MDT-style discussion.
• Orient the ellipse with the long axis parallel to the relaxed skin tension lines or the direction of definitive WLE expansion.

Suspected cSCC

Either incisional biopsy (4–6 mm punch or shave-disc) for histological confirmation before definitive surgery, or primary excisional biopsy with the planned BAD 2020 (Keohane) margin (4 mm for low-risk; 6–10 mm or Mohs for high-risk). Punch through the most representative area, avoiding necrotic crust.

Suspected BCC

Punch biopsy or shave-disc biopsy is acceptable; subtype identification on biopsy guides definitive management (low-risk vs high-risk subtype, Mohs vs WLE). Excisional biopsy with primary closure is appropriate for small, well-defined nodular BCC at low-risk sites.

Suspected Merkel cell carcinoma

Incisional or excisional biopsy with histology and neuroendocrine IHC (CK20 perinuclear-dot, synaptophysin, chromogranin A, TTF1 to exclude metastatic small-cell lung). MCPyV (Merkel cell polyomavirus) large-T antigen IHC is part of standard work-up — contemporary series and meta-analyses put MCPyV positivity in MCC at roughly 70–80% overall, with European pooled estimates around 78%.

Suspected sebaceous / adnexal carcinoma

Punch or incisional biopsy is acceptable; full excision often follows at Mohs. Always trigger the Muir-Torre / Lynch MMR triage (Mallorca Group 2022) on any sebaceous neoplasm — Tier 1 MMR IHC (MLH1, PMS2, MSH2, MSH6), Tier 2 MLH1-promoter methylation for MLH1/PMS2 loss, Tier 3 clinical genetics referral.

Suspected cutaneous lymphoma

Multiple deep punch biopsies (≥ 2 sites if possible) with submission of fresh tissue for flow cytometry where the local pathway supports it, plus standard formalin-fixed tissue for immunohistochemistry and TCR clonality. Refer to a UK supraregional cutaneous lymphoma service for confirmation.

Specimen handling

• Single 10% buffered formalin pot for the majority of skin biopsies. Tissue:formalin ratio ≥ 1:10.
• Orientation — for excisions where it may be possible to re-excise a single incomplete margin, consider orientation marking with a suture. Some pathways use a standardised diagram on the request slip.
• Fresh tissue for flow cytometry in suspected cutaneous lymphoma — coordinate with the receiving lab in advance.
• Avoid crush artefact by handling the specimen at the periphery only, with non-toothed forceps.

Histology request — what to write on the form

A high-quality histology request gives the pathologist context, prevents misclassification, and ensures dataset-aligned reporting:

• Clinical suspicion — name the diagnosis you're testing for, in order of probability
• Anatomical site — including laterality, body region, and (for digits / face) the specific subunit
• Duration and rate of change — onset, recent acceleration
• Excision type — incisional / excisional / punch / shave, with stated margin clearance
• Specimen orientation — markers / sutures / ink, mapped on the form
• Prior treatment — cryotherapy, topical therapy, previous biopsies (can change histology)
• Immunosuppression / OTR status
• Request explicit reporting per the current RCPath dataset for the suspected diagnosis

RCPath datasets

The Royal College of Pathologists publishes structured datasets that drive consistent reporting across UK histopathology services. Current datasets relevant to skin oncology:

Dataset	Year	Key reported items
Melanoma	2022	Breslow, ulceration (definition), mitotic rate, regression, LVI, PNI, margins (mm)
cSCC	2020	Diameter, differentiation, depth, BWH risk factors, PNI sub-criteria, margins
BCC	2020	Subtype (low- vs high-risk), depth, PNI, margins
Merkel cell carcinoma	2022	Size, depth, LVI, PNI, MCPyV status, margins, IHC panel
Soft tissue sarcoma	2020	Subtype, grade, depth, margins, molecular fusion (FISH / RT-PCR)

Ancillary testing

• BRAF V600 mutation testing — in metastatic melanoma to guide TA396 (dabrafenib + trametinib) or TA562 (encorafenib + binimetinib) eligibility; some centres also routinely test stage IIIB+ resected disease for adjuvant decisions.
• MMR immunohistochemistry on sebaceous neoplasms — Mallorca Group 2022 tiered triage.
• MCPyV large-T antigen IHC on suspected Merkel cell carcinoma.
• COL1A1–PDGFB FISH / RT-PCR on suspected DFSP (confirms diagnosis; supports sarcoma-MDT consideration of imatinib in advanced disease).
• TCR / IGH clonality (PCR) on suspected cutaneous T-cell or B-cell lymphoma.
• INI1 (SMARCB1) IHC on suspected epithelioid sarcoma.

MDT review timing

The first MDT discussion typically happens within the FDS 28-day window. Specialist Skin MDTs (SSMDTs) review high-risk and complex cases; Local Skin MDTs (LSMDTs) review most NMSC. Cases mandatorily reviewed at SSMDT include:

• Melanoma stage II+ and any case requiring SLNB
• cSCC with high-risk features (BWH T2b / T3, named-nerve PNI, node-positive, recurrent)
• Merkel cell carcinoma — any case
• Rare adnexal carcinoma
• Cutaneous lymphoma — co-discussed with the regional CTCL service
• Cutaneous sarcoma