Paediatric melanoma

Epidemiology

• UK incidence — uncommon in patients < 20; most paediatric / TYA cases occur in older adolescents rather than pre-pubertal children. Registry figures should be checked directly for any precise age-band split.
• Pre-pubertal melanoma is exceptional; incidence rises sharply in adolescence.
• F>M in adolescents (similar to adult young-onset melanoma).
• Risk factors:
  • Large or giant congenital melanocytic naevi — see monograph; large CMN risk is about 1–2%, while giant CMN carry about 2–5% lifetime melanoma risk (highest with multiple satellites; historical series quoted higher).
  • Familial melanoma syndromes — CDKN2A, CDK4, BAP1, POT1.
  • Xeroderma pigmentosum — see monograph.
  • Multiple atypical naevi.
  • Immunosuppression — paediatric organ transplant, congenital immunodeficiency.
  • Severe sunburn history; intermittent intense UV exposure.
  • Fair skin / red hair / freckling.

Clinical presentation

• Conventional ABCDE criteria perform poorly in children.
• Modified paediatric ABCDE criteria (Cordoro et al., 2013):
  • A — Amelanotic.
  • B — Bleeding / Bump.
  • C — Colour uniformity.
  • D — De novo (any diameter).
  • E — Evolution.
• Common atypical presentations:
  • Amelanotic pink / red papule or nodule mimicking pyogenic granuloma, Spitz naevus, vascular lesion or wart.
  • Rapidly growing "bump" with bleeding.
  • Uniformly coloured small (<6 mm) lesion.
  • Lesion arising within an existing congenital melanocytic naevus — beware "satellite" lesions or atypical macular pigmentation.
• Frequent diagnostic delay — paediatric melanomas are misdiagnosed clinically and pathologically (Spitzoid melanoma vs atypical Spitz tumour vs Spitz naevus is genuinely difficult).

Paediatric melanoma subgroups

• Spitzoid melanoma — the major adolescent subgroup; molecularly distinct from conventional melanoma (kinase fusions in ALK, ROS1, NTRK1, MAP3K8 in ~50% of Spitz family lesions); pathologically challenging.
• Conventional adult-type SSM — older adolescents; behaves like adult melanoma with similar molecular drivers (BRAF, NRAS).
• Congenital melanocytic naevus-associated melanoma — typically arises in the dermis or CNS leptomeninges of giant CMN; NRAS-driven; particularly in the first decade.
• Acral / mucosal melanoma in adolescents — rare but clinically distinctive; KIT mutations.
• Familial melanoma in adolescents — CDKN2A / CDK4 / BAP1.

Management

• Refer to paediatric / TYA cancer service in collaboration with adult cutaneous oncology MDT.
• Diagnostic biopsy — full excisional biopsy with 1–2 mm clinical margin is preferred for any clinically suspicious lesion in a child.
• Histological review by an experienced paediatric / Spitzoid dermatopathologist; consider molecular profiling (CGH, FISH for kinase fusions, methylation profiling) for histologically equivocal lesions.
• Wide local excision and sentinel lymph node biopsy use NICE NG14 stage-based margin and SLNB discussion principles, applied with paediatric / TYA MDT input; SLN biopsy is more often positive in paediatric than adult melanoma but the prognostic significance of SLN positivity is less clear in children.
• Adjuvant immunotherapy (pembrolizumab, nivolumab) — emerging evidence in adolescent melanoma; clinical-trial enrolment encouraged.
• Targeted therapy (BRAF / MEK inhibitor combination) for BRAF-mutant disease in adolescents; NTRK / ALK / ROS1 inhibitor for kinase-fusion-positive Spitzoid melanoma.
• Genetic counselling — consider germline CDKN2A / BAP1 / POT1 / XPC / XPA / XPV testing where family history or clinical features suggest a hereditary syndrome.
• Long-term psychosocial support and dedicated TYA pathway.

Prognosis

Stage-matched survival is broadly comparable to adult melanoma; SLN positivity rate is higher but the prognostic implication is less stark. Adverse factors — congenital giant CMN-associated melanoma (poor prognosis); large primary; ulceration; advanced stage; xeroderma pigmentosum or other DNA-repair syndrome.