Prognostic factors and incidence of primary mucosal melanoma: a population-based study in France

Background: Few population-based studies on the incidence and prognosis of primary mucosal melanoma (PMM) are available. Objectives: The first objective was to evaluate disease-specific survival of PMM, overall and according to specific locations, and to identify prognostic factors. The second objective was to assess the global incidence of PMM compared to cutaneous melanoma and to specify the relative frequency of each affected location. Materials & Methods: A retrospective population-based study of incident PMM diagnosed between 2004 and 2014 was conducted, relying on the regional melanoma registry of the French Champagne-Ardenne region (1.34 million inhabitants). Results: Thirty-nine cases were identified, including 17 head and neck (13 sinonasal and four oral), 12 vulvovaginal, six conjunctival, and four anorectal PMMs. Some 76.9% of cases were revealed by late symptoms. The median disease-specific survival time was 23.9 months and the five-year disease-specific survival rate was 31.8%. Univariate and multivariate analyses led to identification of primary tumour size and the presence of nodal or visceral macrometastases at diagnosis as adverse prognostic factors, while Breslow thickness and ulceration were unreported in 41% of cases and failed to display any prognostic value. Compared to other locations, conjunctival PMMs had a smaller tumour size and better prognosis. The annual incidence rate was 0.18/100,000 and the incidence ratio between PMM and cutaneous melanoma was 1/50. Conclusion: This population-based study confirms the rarity, delayed diagnosis, and severity of PMM, suggesting that improving prognosis will require specific, targeted therapies.