Fig. 4

Histopathological findings. a The boundary of the tumor is delineated with a red line on the macroscopic image. The tumor is localized within epithelial and subcutaneous adipose tissue. The macroscopic image shows extensive infiltration and growth of tumor cells. b At the lower peripheral area, tumor cells are infiltrating into the adipose tissue across the desmoplastic border (black arrow). The infiltrating tumor cells show trabecular, sheet-like, acinar, and nesting growth patterns, with a few ductal carcinomas in situ with comedo necrosis (red dotted circle)