Microscopic description:

Multiple sections show tumor cell nests, solid clusters and glands floating in a sea of lightly staining amorphous mucin. Low grade tumor nuclei with no mitoses. Also seen is a focus of low grade DCIS with calcification.

Gross:

soft, pale, grayish blue, gelatin-like and well circumscribed mass

IHC:

Positive for ER, PR (< 70%) and MUC2, Neuroendocrine markers in 15-50% cases and Negative for HER2

Discussion:

Mucinous carcinomas comprise 0.5% to 3% of breast carcinomas. They are slow growing tumor with clusters of small uniform cells floating in lakes of extracellular mucin. Considered as pure mucinous carcinoma if the tumor has 90% or more mucinous / colloid component. Cases with 75% - 90% mucinous / colloid component are considered a mixed variant with a prognosis worse than pure mucinous carcinoma, and dependent on the grade of the remaining carcinoma component. Usually common in older women (mean age 71 years). 10 year survival for pure form is > 90% (much better than ductal carcinoma NOS)

References:

Dumitru A, Procop A, Iliesiu A, et al. Mucinous Breast Cancer: a Review Study of 5 Year Experience from a Hospital-Based Series of Cases. Maedica (Buchar). 2015;10(1):14–18.

Lei L, Yu X, Chen B, Chen Z, Wang X (2016) Clinicopathological Characteristics of Mucinous Breast Cancer: A Retrospective Analysis of a 10-Year Study. PLoS ONE 11(5): e0155132. https://doi.org/10.1371/journal.pone.0155132

CASE IMAGES