Real-World Evidence of the Prevalence of Driver Mutations in Anorectal Melanoma.

Introduction: Anorectal melanoma is a rare neoplasm with an aggressive behavior and poor prognosis. Recently, recurrent gene mutations related to anorectal melanoma have been identified in a small series of cases, and this holds promise for targeted therapies, analogous to cutaneous melanoma. The purpose of this study was to analyze testing rates and prevalence of mutations in anorectal melanoma in the Dutch population.

Methods: The Netherlands Cancer Registry and the Dutch Nationwide Pathology Databank were queried for all patients with a diagnosis of anorectal melanoma (2009-2019) and for whom a molecular analysis was performed. The genes that were tested and mutations that were reported were recorded. Mutation status was correlated with clinical characteristics.

Results: In the period 2009-2019, 121 patients were diagnosed with anorectal melanoma. A molecular analysis was performed for 81 (67%) using single gene testing and various next-generation sequencing panels. Testing rates increased from 53% in 2009-2012 to 73% in 2016-2019. In 29/81 (36%) analyzed tumors, one or more mutations were reported: mutations in KIT (16/70, 23%), CTNNB1 (3/20, 15%), NRAS (6/60, 10%), BRAF non-V600E (4/74, 5%), GNAS (1/19, 5%), KRAS (1/28, 4%), BRAF V600E (1/74, 1%), and SF3B1 (1/1). In this cohort, a positive correlation was found between BRAF mutation status and age. Mutation status did not correlate with sex, date of diagnosis, tumor stage or surgical treatment. Survival was not influenced by any mutation status.

Conclusion: KIT was the most frequently mutated gene in the 81 analyzed anorectal melanomas in the period 2009-2019. With the increasing testing rates and use of next generation sequencing, the molecular landscape of anorectal melanomas is gradually being revealed. Adoption of broad mutation analysis will reveal potentially actionable targets for treatment of patients with anorectal melanoma.