DOI: https://doi.org/10.36347/sasjs.2026.v12i09.001

Pages: 740-743

Mucinous carcinoma of the breast is a rare special histological subtype of invasive breast carcinoma. The pure form is generally characterized by low-grade morphology, hormone receptor positivity, HER2 negativity, and a favorable clinical outcome. We report the case of a 55-year-old postmenopausal woman with no significant personal medical history and a maternal history of breast cancer who presented with recent-onset erythema and progressively worsening pain in the right breast. Clinical examination revealed a firm, mobile mass in the lower outer quadrant with overlying peau d’orange changes. Breast ultrasonography showed a 30 × 22 mm lobulated lesion classified as BI-RADS 4B. Core needle biopsy demonstrated pure mucinous carcinoma, with a mucinous component exceeding 90%, Nottingham grade 1, no lymphovascular or perineural invasion, estrogen and progesterone receptor positivity, HER2 negativity, and a low Ki-67 index, consistent with a luminal A phenotype. Staging investigations showed no distant disease. Following multidisciplinary discussion, breast-conserving surgery with sentinel lymph node assessment was planned, with adjuvant radiotherapy and endocrine therapy to be considered according to the final surgical pathology. This case highlights the clinical, imaging, and pathological features of pure mucinous carcinoma and provides an opportunity to discuss its current management in light of recent literature.