Abstract

Primary malignant melanoma of the gallbladder is a rare tumor with only approximately 40 cases described in the literature. We report a case of presumed primary malignant melanoma of the gallbladder. A 52-year-old male presented with abdominal pain. A cholecystectomy was performed for presumed acute cholecystitis. Macroscopic examination of the gallbladder revealed a 3.9 x 2.5 x 2.0 cm yellow-brown, friable intraluminal polypoid mass arising from the gallbladder wall. Histopathology revealed nests of large atypical epithelioid cells with pleomorphic vesicular nuclei, prominent nucleoli, cytoplasmic abundant granular brown pigment, and occasional intranuclear pseudoinclusions. The tumor cells demonstrated junctional activity as well as invasion through the muscular propria reaching the subserosa with lymphovascular invasion. Immunohistochemical staining showed S-100, HMB-45, and MART-1 positivity. Molecular testing revealed the absence of KIT mutations, NRAS mutations, or the BRAF V600E mutation. Subsequent clinical investigations were performed including detailed physical examination, colonoscopic, ophthalmologic and dermatologic examinations, and PET CT. The patient was diagnosed with primary malignant melanoma of the gallbladder since no other primary focus of the disease was identified. It remains controversial whether gallbladder involvement of malignant melanoma is primary or metastatic. Proving its existence as a primary tumor remains a challenge. Criteria to establish the gallbladder as a primary site for malignant melanoma have been suggested and include (a) histologic junctional activity in the setting of a (b) solitary, (c) polypoid or papillary tumor within the gallbladder lumen, with (d) absence of synchronous involvement at other sites, and (e) exclusion of other possible primary locations.