A Rare Case of Epithelioid Myofibroblastoma of Breast Mimicking Lobular Carcinoma on Trucut Biopsy: a Diagnostic Pitfall and Literature Review.

Epithelioid myofibroblastoma of the breast is a rare benign stromal tumor occurring in the postmenopausal females and elderly males. We report one such case in a 65-year-old female who underwent trucut biopsy from a well-defined right breast lump, which was misinterpreted as invasive lobular carcinoma on histology. Tumor showed mild to moderately pleomorphic tumor cells arranged in single file pattern, loosely dispersed and focally in sheets with inconspicuous nucleoli embedded in a fibrotic and hyalinized stroma. Immunohistochemistry for E-cadherin was negative further substantiating the morphological diagnosis. However, mastectomy specimen revealed it to be a case of epithelioid myofibroblastoma with the help of a large panel of immunohistochemical stains. In this report, we emphasize on the challenges of establishing this rare diagnosis mimicking lobular carcinoma, a diagnostic pitfall on trucut biopsy. © Indian Association of Surgical Oncology 2021.