Mucosal melanoma
Sinonasal melanoma; oral melanoma; anorectal melanoma; vulval / vaginal melanoma
Mucosal melanoma is a rare and biologically distinct melanoma arising from melanocytes in the mucosal surfaces of the head and neck (sinonasal, oral), anorectum and female genital tract. It carries a substantially worse prognosis than cutaneous melanoma — late presentation, anatomically restricted surgical margins, distinct molecular biology (KIT and NRAS mutations more common; BRAF less common), and limited evidence base for adjuvant therapy.
Epidemiology
Mucosal melanoma represents approximately 1% of all melanoma. Annual UK incidence is small (a few hundred cases). Median age 60–70. Female predominance in vulvovaginal and anorectal disease; near-equal sex ratio in head and neck. No significant ethnic variation in incidence.
Sites & presentation
Head and neck (~55%)
- Sinonasal — epistaxis, nasal obstruction, sometimes a visible polypoid mass.
- Oral cavity — pigmented or amelanotic lesion of palate or gingiva, often discovered incidentally on dental review.
Anorectal (~24%)
- Anal canal mass, bleeding, change in bowel habit; often misdiagnosed as haemorrhoids initially.
Vulvovaginal (~18%)
- Vulval pigmented lesion or bleeding; vaginal melanoma usually presents with PMB or vaginal discharge.
Other
- Conjunctival, urinary tract, biliary, oesophageal — very rare.
Diagnosis
Biopsy of the mucosal lesion. Histology and immunohistochemistry as for cutaneous melanoma (S100, SOX10, MART-1, HMB-45). Molecular profiling: KIT mutation (15–20%), NRAS, BRAF (less common than cutaneous). Staging imaging is more extensive than for cutaneous — MRI of primary site, PET-CT for systemic staging.
Staging
Site-specific staging systems are used. Head and neck mucosal melanoma uses AJCC 8 mucosal H&N staging, which by design begins at T3 (there is no T1 or T2 category in this scheme, reflecting the typically advanced stage at diagnosis). Cutaneous melanoma arising on hair-bearing vulval or perianal skin should be staged as cutaneous melanoma. True anorectal and vulvovaginal mucosal melanomas do not have a single universally accepted validated AJCC mucosal TNM; MDTs commonly record local / regional / distant extent, nodal basins, metastatic status and site-specific gynae / colorectal anatomical staging details.
Management
Surgery
- Wide local excision with negative margins where feasible — anatomical constraints often preclude wide margins.
- Head and neck: endoscopic resection for sinonasal disease; oral excision with reconstruction.
- Anorectal: local excision for early disease; abdominoperineal resection rarely improves outcomes.
- Vulval: first distinguish hair-bearing vulval skin melanoma from true mucosal vulval / vaginal melanoma. Hair-bearing skin lesions follow the cutaneous melanoma pathway; mucosal disease is managed through joint gynae-oncology and melanoma MDTs with radical local excision where feasible and selective SLNB discussion.
Adjuvant radiotherapy
Improves local control after surgery for head and neck mucosal melanoma; no clear OS benefit. Often used given high local recurrence risk.
Systemic therapy
- Immune checkpoint inhibitors — response rates lower than cutaneous melanoma but still meaningful (~20% with monotherapy, higher with combinations).
- KIT inhibitors (imatinib, nilotinib) for KIT-mutant disease — modest activity.
- BRAF/MEK inhibitors only if BRAF-mutant (uncommon).
Prognosis
5-year overall survival is approximately 25–40% — substantially worse than cutaneous melanoma at any stage. Locoregional and distant recurrence are common. Specialist multidisciplinary care at high-volume centres improves outcomes.
References
- Carvajal RD et al. Mucosal melanoma: a clinically and biologically unique disease entity. J Natl Compr Canc Netw; 2012.
- Tacastacas JD et al. Update on primary mucosal melanoma. J Am Acad Dermatol; 2014.
- Yang J et al. Treatment of mucosal melanoma with immune checkpoint inhibitors. Cancer Treat Rev; 2020.
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