Background Mucinous carcinoma of the breast (MCB) is a rare histological subtype accounting for approximately 2% of all breast cancers, and it is characterized by abundant extracellular mucin production, indolent clinical behavior, and a favorable prognosis compared with other invasive breast carcinomas. Early and accurate recognition is essential due to its distinct pathological and immunohistochemical features. Case Presentation A 50‐year‐old woman with no significant medical or family history presented with a palpable mass in her right breast, so she underwent breast screening. The imaging revealed multiple irregular nodular lesions with clustered microcalcifications in the right breast (BI‐RADS 4C), so she underwent a right modified radical mastectomy with axillary dissection. However, histopathological examination confirmed a well‐differentiated pure mucinous carcinoma (> 90% mucinous component, Nottingham Grade I) without lymphovascular invasion or nodal metastasis (0/13). The tumor was ER/PR–positive, HER2‐negative, with a low Ki‐67 index (3%), and was completely excised with negative margins. Discussion Pure MCB exhibits favorable biological behavior and excellent outcomes, particularly when accurately diagnosed through histopathological and immunohistochemical evaluation. Conclusion Pure MCB is a rare, low‐grade tumor with distinct pathological features. Accurate diagnosis and complete surgical excision are essential for optimal management, as patients typically achieve excellent long‐term outcomes.
Hendi et al. (Thu,) studied this question.