Summary Mucinous micropapillary carcinoma of the breast, also described as “pure mucinous carcinoma with micropapillary pattern,” has recently come to attention as an unusual form of invasive breast ...cancer exhibiting dual mucinous and micropapillary differentiation. Despite increasing awareness of this morphologic variant, its clinical significance has not yet been elucidated. Here, we present 15 additional examples of these rare tumors to highlight some important differences between mucinous micropapillary carcinoma of the breast and ordinary pure mucinous carcinomas. The key features of mucinous micropapillary carcinoma of the breast included ( a ) largely or entirely mucinous appearance (>90% mucinous morphology), ( b ) distinctive micropapillary arrangement of the neoplastic cells, ( c ) intermediate to high nuclear grade, ( d ) “hobnail” cells, and ( e ) frequent psammomatous calcifications. In contrast to ordinary pure mucinous carcinomas, 20% of mucinous micropapillary carcinomas of the breast were characterized by human epidermal growth factor receptor 2 positivity, and 23% were p53 positive. More than half of mucinous micropapillary carcinomas of the breast (60%) demonstrated lymphovascular invasion, sometimes extensive. Synchronous axillary lymph node metastases were detected in 33% of patients and, on 2 occasions, involved more than 10 nodes. With a median follow-up of 4.5 years, we identified 1 patient (7%) with chest wall recurrence of mucinous micropapillary carcinoma of the breast after mastectomy. We conclude that mucinous micropapillary carcinomas of the breast constitute a clinically aggressive subset of mucin-producing breast carcinomas characterized by an increased capacity for lymphatic invasion and regional lymph node metastasis, reflective of their dual phenotype. Recognition of the morphologic and biologic heterogeneity within breast cancer subtypes should allow for a more accurate classification of the individual tumors and better patient stratification for treatment.
Abstract Acinic cell carcinoma of breast is a rare subtype of triple negative breast carcinoma and demonstrates extensive morphologic overlap with acinic cell carcinoma of the salivary gland. In this ...study, we perform a detailed morphologic and immunohistochemical description of two cases of this rare entity, and undertake a comprehensive review of all reported cases of breast acinic cell carcinoma in the English language literature to date. One third of reported cases of breast acinic cell carcinoma have been associated with the presence of a ductal carcinoma not otherwise specified (NOS) component, which is frequently poorly differentiated. Breast acinic cell carcinoma can demonstrate focal morphologic features similar to microglandular adenosis; these areas are frequently negative for collagen IV and laminin on immunohistochemistry. The true relationship between these two entities remains unclear, but we advocate that microglandular adenosis-like areas at the periphery of a breast acinic cell carcinoma should be considered part of the carcinomatous process and re-excised if this process extends to the initial surgical margins.
Invasive breast cancers constitute a heterogeneous group of lesions. Although the most common types are ductal and lobular, this distinction is not meant to indicate the site of origin within the ...mammary ductal system. The main purpose of the identification of specific types of invasive breast carcinoma is to refine the prediction of likely behavior and response to treatment also offered by the other major prognostic factors, including lymph node stage, histologic grade, tumor size, and lymphovascular invasion.
To the Editor: Dr Shet's letter raises an interesting question as to whether mucinous breast carcinoma is a distinct clinicopathologic entity or merely an umbrella term for mucin-producing papillary, ...solid papillary, and micropapillary tumors.
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