Background: Mucinous carcinoma of the breast is a rare pathological entity comprising only 4% of breast tumors. The classic teaching describes this tumor as prototypically an oval dense mass on mammography, demonstrating benign features, exhibiting non-aggressive behavior, and usually limited to elderly patients. In fact, mucinous carcinomas are quite variable in appearance. More importantly, on pathologic evaluation, mucinous carcinomas may be categorized into different subtypes with divergent behavior. These subtypes include Pure Mucinous Carcinoma (PMC), defined as invasive carcinoma consisting of more than 90% mucin, and yielding a 90% overall survival; and Mixed Mucinous Carcinoma (MMC), consisting of < 90% mucin and mostly micropapillary ductal and lobular components, with a higher risk of metastases. Although these two subtypes are distinct entities with different prognoses, they may have overlapping imaging features.
Learning Objectives: The goal of this exhibit is to describe the various imaging features of pure and mixed mucinous carcinoma of the breast on mammogram and ultrasound, and highlight the importance of radiologic/pathological concordance at the time of diagnosis to estimate prognosis, inform treatment, and guide surveillance.
Abstract Content/Results: Both pure and mixed mucinous carcinoma may present as masses or calcifications. Suspicious calcifications, often coarse heterogenous in morphology, should be identified and biopsied, as these correlate with worse prognosis, especially in mixed subtypes. Through a limited case series we will present different atypical presentations of mucinous breast carcinomas on mammography.
Conclusion: Redesign of classic teaching of mucinous carcinomas of the breast is crucial to confidently determine concordance at the time of biopsy. Differentiation of pure and mixed subtypes is necessary to tailor appropriate definitive treatment and surveillance.
