Mucoepidermoid Carcinoma of the Gallbladder: A Case-Based Study of an Extremely Rare Tumor Highlighting the Role of Immunohistochemical Profiling.

Mucoepidermoid carcinoma (MEC) is rarely reported in the hepatobiliary system. In this article, we detail the first case of MEC arising from the gallbladder, presenting in a 50-year-old male. Imaging and gross examination showed a large mass in the gallbladder fossa infiltrating the liver. This microscopically displayed the classical morphology of MEC, which was confirmed on dual immunostain for p63 and CK7 and histochemical staining for mucin. MUC and p53 immunoexpression patterns suggested a poor prognosis. The patient succumbed to the disease with liver metastasis within 6 months. The cytomorphology of the metastatic lesion is also presented. Differences in the stem cell niches in the gallbladder and the rest of the biliary tract may possibly indicate the reason for the rarity of this tumor in the gallbladder. A possibly aggressive biological behavior of the gallbladder MEC necessitates its distinction from entities like the adenosquamous carcinoma.