Melanoma margins (NICE NG14)

Stage 0 (in situ) — at least 0.5 cm peripheral margin; consider staged excision / Mohs with immunostains or a wider clinical margin for lentigo maligna, head-and-neck disease or large ill-defined lesions.
Stage I — 1 cm clinical margin. This includes pT1 disease and pT2a disease (1.01–2.0 mm without ulceration).
Stage II — 2 cm clinical margin. This includes pT2b disease (1.01–2.0 mm with ulceration), pT3 and pT4 disease; 1 cm is reserved for situations where a 2 cm margin would cause unacceptable disfigurement or morbidity.
Margins are measured clinically from the visible lesion or biopsy scar, perpendicular to the skin, and confirmed histologically. Deep margin to underlying fascia (not through it) for invasive disease.

cSCC margins (BAD 2020)

Low-risk cSCC — 4 mm peripheral margin.
High-risk cSCC — 6 mm peripheral margin.
Very high-risk cSCC (BWH T2b/T3, recurrent, immunosuppressed) — consider 10 mm or Mohs micrographic surgery.
Deep margin to subcutis ± fascia depending on tumour depth and anatomic site.

Low-risk BCC (well-defined nodular/superficial, < 2 cm, low-risk site) — 4 mm peripheral margin.
High-risk BCC (morphoeic / infiltrative / micronodular subtype, recurrent, immunosuppressed, H-zone, > 2 cm) — 5 mm minimum; Mohs micrographic surgery preferred where access exists.
Deep margin to subcutis.

Photograph the lesion / scar at consent and at planning.
Mark the visible lesion / scar and the planned margin with a surgical pen with the patient sitting up; check tension and orientation; redraw with the patient supine if needed.
Plan the closure before incision (primary, advancement, transposition, rotation, graft) — see Reconstruction atlas.
Local anaesthesia with 1% lidocaine + adrenaline (avoid adrenaline on digits and end-organs).
Anti-coagulation, aspirin and clopidogrel — discuss patient-specific risk; most skin excisions can continue antiplatelets without significant bleeding risk.

Sharp dermal-edge incision perpendicular to the skin surface — bevelled cuts compromise margin assessment.
Deep plane chosen by tumour type and anatomy — fascia is generally safe but not always necessary for thin lesions; for melanoma the deep margin is the fascia of the muscle below, included only if invaded.
Haemostasis with bipolar or fine cautery; avoid charring the specimen edge.
Orient the specimen with a suture marker only where re-excision of a single involved margin is plausible (e.g. on the face where margin sparing matters) — over-orientation makes pathology harder.
Closure under no tension — undermining and layered closure according to site, depth and tension.

Specimen sent in 10% formalin labelled with patient identifiers, site, orientation if marked, and the tumour type / clinical question.
Histopathology reports peripheral and deep margin clearance in millimetres and records subtype, depth, ulceration, mitotic rate, lymphovascular invasion and perineural invasion as relevant.
Incomplete or close margins — MDT discussion; options include re-excision, Mohs (for non-melanoma), adjuvant radiotherapy and active surveillance.
Re-excise via the original scar to preserve cosmesis and avoid creating new margin disturbance.