Background: A 79-year-old man presented to his primary care physician with a 2-month history of pruritus ani and a pigmented nodular lesion was discovered in the posterior rectum. The patient had no other symptoms, or any family history of malignancy.
Investigations: Physical examination; excisional biopsy; CT scan of the chest, abdomen and pelvis; lung biopsy; blood tests; tumor immunohistochemistry for KIT, vascular endothelial growth factor platelet-derived growth factor receptor alpha and beta, and mismatch-repair proteins MLH1, MSH2, and MSH6; and KIT and BRAF tumor genotyping.
Diagnosis: Stage IV M1b metastatic anal mucosal melanoma.
Management: Wide local excision with mucosal advancement of the rectal wall, external-beam radiation, and sorafenib-temozolomide therapy.