A rare case of polypoid primary anorectal melanoma with subsequent giant stomach metastasis: a gastrointestinal involvement of both primary and metastatic mucosal melanoma

Melanoma can involve the gastrointestinal apparatus as both primary and metastatic lesions. Primary anorectal mucosal melanoma (ARMM) and metastatic gastric melanoma are rare entities and usually resulted in a poor prognosis. We presented a case of a 61-year-old man who after the complete excision of an ARMM developed a gastric metastasis after almost three years form the complete tumour excision. Upon esophagogastroduodenoscopy, a giant ulcered mass resulted in melanoma metastasis. The patient underwent a near-total gastrectomy. After five months of follow-up, the patient is disease-free. The incidence of ARMMs is increasing, highlighting the necessity of new prevention and treatment strategies in order to achieve a better prognosis for these patients. There are no known risk factor for ARMMs but surgery, together with the combination of anti-CTLA-4 and anti-PD-1 antibodies, are promising therapeutic options. Early and aggressive treatments are required, together with a strict multidisciplinary approach.