Pure Mucinous Carcinoma of the Breast: Case Report

Introduction: Pure mucinous carcinoma (PMC) of the breast is a rare histological subtype (<2% of breast cancers), typically diagnosed in postmenopausal women. Its presentation in younger patients is exceptional, and its diagnostic management poses challenges due to nonspecific imaging characteristics. Case presentation: A 42-year-old woman with no relevant medical history presented with a palpable mass in the left breast during a routine gynecological check-up. The initial mammogram revealed a hypodense, microlobulated lesion (2.17 × 1.5 cm), classified as BIRADS 3. After 6 months, ultrasound showed a 20% increase in size (2.6 × 1.8 cm), with cystic areas and reclassification to BIRADS 4A. Core needle biopsy confirmed PMC. A radical mastectomy with sentinel lymph node biopsy was performed (negative for metastasis), and adjuvant radiotherapy was not required. Discussion: This case contrasts with literature reporting an average age at diagnosis of 70 years. Rapid tumor growth (20% in 6 months) is atypical for PMC, which usually follows an indolent course. The imaging reclassification from BIRADS 3 to 4A highlights the importance of close follow-up and biopsy in the presence of morphological changes, even when initial suspicion is low. The absence of lymph node involvement aligns with the favorable prognosis typically reported for PMC. Conclusion: PMC should be included in the differential diagnosis of breast masses regardless of patient age. Dynamic clinico-radiological correlation and early histological confirmation are essential for timely management. Reporting atypical cases contributes to optimizing protocols for these uncommon tumors.