An 82-year-old patient, diagnosed after a study of normocytic-normochromic anaemia by colonoscopy of neoplasia of the right colon. Both the histological and cytological studies diagnosed MM. After an exhaustive extension study, which included a thoracoabdominal CT scan, abdominal ultrasound, dermatological examination (including exeresis and study of two nevi that ruled out MM), fundus study and anorectal examination, the patient underwent surgery and a right hemicolectomy.
The anatomopathological study of the resection specimen confirmed the presence of a polypoid and ulcerated MM measuring 11 cm in diameter at the level of the ascending colon, which invaded the submucosa and focally the muscular layer. Numerous tumour cells contained melanin and immunohistochemistry was positive for S-100 protein and HMB45. Of the 30 lymph nodes resected, 2 had metastases. The patient followed a good postoperative course, being alive with no evidence of disease 4, 5 years after surgery.