Luminal-Type Invasive Carcinoma in Association With Microglandular Adenosis/Atypical Microglandular Adenosis: A Case Report and Molecular Comparison.

Microglandular adenosis (MGA) is a proliferative breast lesion composed of small, uniform glands lacking a myoepithelial cell layer while still invested by the basement membrane. The glands percolate haphazardly through the breast parenchyma rather than maintaining a lobular architecture, typical of other forms of adenosis.MGA is a benign lesion though atypical forms have been well described, often in close association with carcinoma. MGA, atypical MGA (AMGA), and the vast majority of MGA-associated carcinomas (MGACA) are negative for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 (HER2) by immunohistochemistry. In light of these findings and early molecular studies, MGA is hypothesized to represent a clonal process and nonobligate precursor of basal-type breast carcinomas. We present the case of a 58-year-old woman and the first published molecular comparison of a luminal-type invasive ductal carcinoma with its associated MGA/AMGA. Analysis of small nucleotide variants (SNVs) revealed that 63% of the SNVs identified in the MGA were present in the AMGA while only 10% of them were present in the MGACA, suggesting a direct relationship between MGA and AMGA but not MGA and MGACA.