Mucinous Carcinoma of the Breast With Neuroendocrine Differentiation: A Case Report of Cyto-Histopathology Findings

Mucinous breast carcinoma is a rare neoplasm. A minority of breast neoplasms exhibit a mucinous component, with purely mucinous cases being less frequent. It is more typically found in postmenopausal women. The etiology is multifactorial and involves dietary factors, reproductive factors, and hormonal factors. Mucinous carcinoma can grow to a large size at the time of diagnosis, although it typically grows slowly and palpable. Transcriptomic genetic studies have explained that mucinous tumors are of luminal A molecular subtype. Mucinous A tumors have different transcriptome characteristics than mucinous B tumors, which have a gene expression pattern resembling neuroendocrine (NE) carcinomas. Diagnosis of mucinous carcinoma with NE differentiation by fine needle aspiration cytology (FNAC) is reported infrequently. Histopathology is mandatory in the evaluation of mucinous breast carcinoma. NE carcinoma of the breast is an underestimated subtype of BC which has characteristics of heterogenicity, rarity, and poor differentiation. In this instance, we present a case of breast carcinoma exhibiting NE differentiation. A postmenopausal woman aged 63, with no family history of breast cancer, presented with a firm mass in the upper lateral quadrant of her right breast. This lump, causing discomfort for the past two years, was accompanied by nipple retraction and the discharge of bloody fluid. The clinical examination revealed the palpable presence of the lump. Ultrasonography-guided FNAC suggested Mucinous breast carcinoma with NE differentiation. The patient underwent a modified radical mastectomy, and the tissue was evaluated by immunohistochemistry which confirmed the diagnosis.