Melanoma is derived from malignancies of melanocytes. Anorectal melanoma differs significantly from cutaneous melanoma in clinical presentation, genetic profile, staging system, and response to treatment. Anorectal melanoma is seldom diagnosed because most melanoma occurrences are found in the skin tissues. Here, we report 1 case of advanced anorectal melanoma, including its clinical presentation, laboratory findings, imaging, surgical treatment, and pathology. The patient complained of hematochezia and tenesmus. Colonoscopy, computed tomography (CT) scan and digital rectal examination (DRE) revealed a mass near the pectinate line. The patient underwent proctectomy along with colostomy, and subsequent pathological examinations suggested anorectal melanoma with serosa involvement (positive markers: S100, HMB-45, etc.). Evidence-based analyses (single-nucleotide polymorphism (SNPs) and programmed death-ligand 1 (PD-L1) expression) were conducted on the tumor tissue to identify the sensitivity to adjuvant therapies. SNP tests suggested no definite efficacies of commonly used chemotherapeutic agents, with PD-L1 expression implying poor sensitivity to PD-L1 inhibitors. The postoperative recovery was uneventful and the patient was discharged on day 7 after admission. However, the patient refused adjuvant therapies and died 11 months after surgery. In conclusion, anorectal melanoma tends to be mistaken for other common diseases in this region owing to its non-specific clinical presentations. Multidisciplinary treatments are recommended to yield the best possible outcome, despite poor prognosis.
Keywords: Anorectal melanoma; adjuvant therapy; case report.