Primary Multifocal Neuroendocrine Tumor of the Breast: A Diagnostic Dilemma.

Primary neuroendocrine neoplasms (NENs) of the breast are extremely rare and diagnostically challenging tumors. We are reporting a female patient in her 40s with progressively enlarging, painless lumps measuring 30 mm and 15 mm in the upper and lower inner quadrants of the right breast for three months. Mammography reported it as the Breast Imaging Reporting and Data System (BIRADS) IVC lesion. A fine needle aspiration cytology (FNAC) done on the right breast lump and right axillary lymph node was reported as carcinoma with metastasis. Subsequent biopsy and immunohistochemistry (IHC) were reported as carcinoma with neuroendocrine differentiation. A right modified radical mastectomy with axillary lymph nodal dissection confirmed a multifocal primary neuroendocrine tumor (NET) of the breast with nodal metastasis. Accurate diagnosis of a primary NET of the breast requires clinico-radiological exclusion of a metastatic tumor. Other breast carcinomas, such as solid papillary carcinoma and hypercellular mucinous carcinoma, which are known to express NE differentiation, also need exclusion.