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MelanomaStage 0 / TisICD-10 D03.x · AJCC 8 Tis

Melanoma in situ

MIS · Stage 0 melanoma · in-situ melanoma · level I melanoma

Melanoma in situ (MIS) is malignant proliferation of atypical melanocytes confined to the epidermis, without invasion through the basement membrane. It is classified AJCC 8 Tis (Stage 0) and carries a near-100% melanoma-specific survival when completely excised. Recognised clinical and histological subtypes include lentigo maligna (chronically sun-damaged skin), superficial spreading MIS, acral MIS and mucosal MIS. NICE NG14 says to consider at least a 5 mm clinical margin for stage 0 melanoma; in practice, lentigo maligna, head-and-neck disease, large lesions and ill-defined lesions often need the upper end of the 5-10 mm range or staged margin-controlled excision, with complete clearance confirmed before reconstruction in cosmetically sensitive areas.

CurrentLast reviewed 21 May 2026

Classification and subtypes

  • Lentigo maligna (LM): chronically sun-damaged elderly skin (head, neck, dorsal hands); slow-growing irregular pigmented patch. Separate monograph covers detail.
  • Superficial spreading MIS: trunk, limbs; the in-situ phase of superficial spreading melanoma.
  • Acral lentiginous MIS: palms, soles, subungual; longitudinal melanonychia / acral pigmented macule with atypical dermoscopy.
  • Mucosal MIS: oral, conjunctival, vulval, anal mucosa; difficult diagnosis owing to absence of dermoscopic features.
  • Naevoid MIS: closely resembles a naevus clinically — easily missed.
  • Desmoplastic MIS (in-situ component of desmoplastic melanoma).

Pathology

  • Proliferation of atypical melanocytes confined to the epidermis.
  • Architectural features:
    • Increased melanocyte density along basal layer.
    • Pagetoid (upward) scatter of melanocytes.
    • Confluence / nesting at the dermo-epidermal junction.
    • Extension along adnexal epithelium (follicular / eccrine).
  • Cytological features:
    • Nuclear atypia, pleomorphism, prominent nucleoli.
    • Hyperchromasia, increased nuclear-to-cytoplasmic ratio.
  • No dermal invasion (defining feature; transection requires comment).
  • IHC: Melan-A / MART-1, S100, SOX10, HMB-45, MITF, PRAME (diffuse PRAME strongly supports melanoma).
  • Molecular: BRAF (typically wild-type in LM; V600 mutation in SSM-MIS); NRAS; KIT (acral / mucosal).

AJCC 8 staging

  • pTis — melanoma in situ.
  • Stage 0 — Tis N0 M0.
  • Near-100% 10-year melanoma-specific survival following complete excision.
  • No SLNB required.
  • No staging imaging required (unless field-cancerisation surveillance for dysplastic-naevus / familial melanoma context).

Differentials

  • Solar lentigo — flat, uniform tan macule; classic moth-eaten dermoscopic pattern.
  • Lentigo simplex — well-demarcated, even pigment.
  • Pigmented actinic keratosis — keratotic surface; PAK can co-exist on LM background.
  • Seborrhoeic keratosis (pigmented variant) — milia-like cysts, comedo-like openings on dermoscopy.
  • Pigmented BCC — pearly border; arborising vessels; leaf-like and spoke-wheel structures.
  • Ink-spot lentigo — see separate monograph.
  • Atypical / dysplastic naevus — diagnostic biopsy required.
  • Lichen planus-like keratosis — regressing lichenoid lesion.
  • Pigmented Bowen disease — keratotic plaque; histology.

Investigations

  • Dermoscopy: facial site features (pseudo-network obliteration, asymmetric pigmented follicular openings, slate-grey dots, rhomboidal structures), atypical pigment network on non-facial skin.
  • Reflectance confocal microscopy (RCM): where available; high diagnostic accuracy for LM and mapping margins.
  • Skin biopsy:
    • Excisional biopsy with 2 mm margin preferred (NICE NG14) — provides complete histology and avoids sampling error.
    • Punch / incisional only if size / site precludes excisional.
    • Avoid shave biopsy in suspected pigmented melanoma — transection compromises Breslow.
  • Mapping biopsies: for large LM lesions where complete excisional biopsy not feasible; multiple punches at peripheral / clinically uncertain edges.

Management (NICE NG14)

  • Wide local excision margins:
    • Non-LM melanoma in situ: 5 mm clinical margin.
    • Lentigo maligna: 5-10 mm clinical margin; 10 mm typically used for head & neck because of subclinical extension along adnexa.
  • Confirm complete excision before definitive reconstruction in cosmetically sensitive areas (face) — wait for permanent paraffin; consider staged excision with intervening delay.
  • Mohs / slow-Mohs / staged excision: increasingly used for LM on face — better margin control with less tissue loss. Permanent paraffin in en-face Mohs preferred over frozen section (which is unreliable for melanocytic lesions).
  • Non-surgical options (for unfit / inoperable / extensive LM):
    • Topical imiquimod 5% — off-label, evidence emerging; ~70-80% clinical clearance; recurrence rate uncertain; not a substitute for excision in fit patients.
    • Radiotherapy — an option for lentigo maligna where surgery is unsuitable, delivered as low-energy / superficial (kilovoltage; Miescher-type) radiotherapy by clinical oncology, with regimen and dose individualised (definitive or adjuvant).
    • Watchful waiting in selected very elderly / frail patients.
  • SLNB: not indicated for melanoma in situ.
  • Staging imaging: not routinely indicated.
  • Follow-up (NICE NG14):
    • Stage 0: a single advice/education appointment during the first year, then discharge with self-examination and photoprotection advice (NICE NG14 recommendation 1.9.4) — consistent with the cutaneous melanoma page. Ongoing surveillance only if other melanoma risk factors are present (e.g. multiple atypical naevi, FAMMM).
    • Full skin examination at each visit.
    • Counsel on self-skin examination and photoprotection.
    • Source-checked 18 May 2026 against NICE NG14, last updated 27 July 2022.

Practical points

  • Always confirm complete excision before reconstruction in cosmetically sensitive sites — staged approach preferred.
  • Communicate with pathologist about subclinical / adnexal extension expected in LM.
  • Discuss patient about second primary risk (~5-10% lifetime); UV photoprotection counselling.
  • Family history: if ≥3 affected relatives on the same side of the family (or 3 primary melanomas in one person) → familial melanoma referral and CDKN2A / MITF E318K testing.
  • Communicate dataset-compliant pathology to MDT; clarify whether SLNB triggered if invasion identified on permanent.
  • Refer for psychology / support given small but real recurrence anxiety; signpost Macmillan resources.

References

  1. NICE NG14. Melanoma: assessment and management. London: NICE; 2015 (last updated 27 July 2022).
  2. NICE NG14. Melanoma: assessment and management. London: NICE; 2022.
  3. Swetter SM et al. NCCN guidelines: melanoma — cutaneous. NCCN; 2024.
  4. Read T et al. In situ melanomas. Dermatol Clin. 2019;37:259-269.
  5. Powell AM et al. Imiquimod and lentigo maligna: a search for prognostic features in a clinicopathological study of 30 patients. Br J Dermatol. 2009;160:994-998.
  6. Gershenwald JE et al. Melanoma staging: AJCC 8th edition. CA Cancer J Clin. 2017;67:472-492.

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