Primary gallbladder melanoma - a rare entity or a diagnostic pitfall?

Primary gastrointestinal (GI) melanoma is an exceptionally rare and controversial diagnostic entity. Because the mucosa of the gallbladder, stomach, small bowel, and large bowel is not considered a common site of melanocytic proliferation, most GI melanomas are regarded as metastatic lesions originating from a primary cutaneous melanoma. Whether some of these tumors may truly arise primarily in GI sites remains a matter of debate. The diagnosis is further complicated by the possibility of occult, clinically subtle, or amelanotic cutaneous melanomas that may remain unrecognized until advanced metastatic disease becomes symptomatic. In addition, spontaneous regression of the primary cutaneous lesion may lead to complete or partial disappearance of the original tumor, creating further diagnostic uncertainty. We performed a literature review focused on GI and gallbladder melanoma, with emphasis on the distinction between primary and metastatic lesions and the role of spontaneous regression. In addition, we analyzed all cases of GI and gallbladder melanoma diagnosed in our department during the last five years. Three cases were identified: one gallbladder melanoma and two small bowel melanomas. These cases illustrated distinct clinical scenarios, including GI bleeding associated with gallbladder involvement, amelanotic ileal melanoma, and intussusception caused by metastatic melanoma from a known cutaneous primary lesion. Our findings support the need for cautious interpretation when diagnosing primary GI melanoma. Metastatic disease from occult, regressed, or previously undiagnosed cutaneous melanoma should always be carefully excluded through multidisciplinary clinicopathological evaluation.