Tubular-Trabecular Type Basal Cell Adenoma of the Parotid Gland: A Patient Report

Basal cell adenoma (BCA) is an uncommon benign salivary gland neoplasm that includes isomorphic basaloid cells. We report on a female patient with BCA that developed in the right parotid gland in her 50s. The present patient demonstrated a few tumor nests in the fibrous capsule, and her tumor was larger than usual. These facts made us suspect of malignancy. Histopathologically, the tumor was characterized by multiple duct-like structures and tubular-trabecular masses composed of small isomorphic cells with hyperchromatic, round nuclei and an eosinophilic cytoplasm. It was difficult to determine whether the ductal structures noted in the tumor capsule were invasive. By immunohistochemistry, tumor cells of the tubular nests were positive for cytokeratin 7 and that the outer cells of tubular nests were positive for alpha smooth muscle actin (αSMA) and calponin. Tumor cells were immuno-negative for S-100 protein and glial fibrillary acidic protein. The Ki-67 labeling scores of the cells were extremely low (< 1%). We could achieve an accurate diagnosis of BCA by immunohistochemistry with MIB-1 and other markers.