Clinicopathological and Molecular Characteristics of Mammary Adenoid Cystic Carcinoma With Adipocytic Differentiation With Emphasis on the Identification of a Novel BRAF Mutation

Histopathological features of primary mammary adenoid cystic carcinoma with extensive adipocytic differentiation. A: The tumor tissue exhibited two morphologically distinct components: classic solid and cribriform neoplastic glands in a desmoplastic background (central portion; lower half) and atypical tumor cell nests within adipose tissue (peripheral portion; upper half). B: At the periphery, individual tumor cell nests possessed a periductal cuff of cellular myxoid stroma and adipose tissue (right lower corner). Some nests exhibited spindle-shaped stromal cells only in the remaining myxoid stroma (upper half). A few spindle-shaped cells scattered and merged with adipocytes in the remaining area can be seen. C and D: The tumor nests within the nests, peritumoral spindle-shaped cells, and scattered slender spindle-shaped cells embedded in adipose tissue were positive for cytokeratin 5/6 (C) and smooth muscle actin (D). Staining method: A and B, hematoxylin and eosin; C and D, polymer method. Original magnification: A, 40×; B, 100×; C, 100×; D, 200×.