Fibroadenoma of the gallbladder with borderline malignancy: a poorly recognized gallbladder tumor.

Fibroadenoma of the gallbladder is extremely rare tumor, with only two cases reported in the world. It is characterized by abundant loose edematous connective tissue, glandular structure, polypoid structure covered by epithelia, and a filamentous pedicle. We report a case of 78-year-old woman histopathologically diagnosed after surgery. Macroscopically, the tumor was a dark-greenish solid mass with a short stalk, filling the gallbladder cavity, and it measured 11.5 x 4.0 x 3.5 cm in diameter. Microscopically, the tumor was composed of abundant loose stroma and a glandular component. Some of the glandular cells had hyperchromatic nuclei with disturbed polarity and were positively stained by p53 (30%) and Ki-67 (30-40%). Part of the stromal component revealed hypercellularity with an irregular nucleus, mitosis (2-3 cells/10 high-power fields), and positivity for Ki-67 (20%) and p53 (50%). We diagnosed this peculiar tumor as "fibroadenoma of the gallbladder with borderline malignancy". We present the details of this extremely rare case and discuss the pathological findings, comparing them to those in the two previously reported cases and to carcinosarcoma of gallbladder.