Microglandular adenosis associated with invasive breast carcinoma: Tertiary care oncology centre experience of an under-recognized entity.

Invasive breast carcinoma (IBC) arising within microglandular adenosis (MGA-CA), a rarity, is usually triple-negative (TNBC). TNBC burden is high in the South-Asian region, but little is known about MGA-CA. Herein, we analyze the clinicopathological spectrum of MGA-CA diagnosed at our tertiary care oncology center. Twenty-three cases of MGA-CA from 2005 to 2024 were collected. Clinicopathological parameters, including immunohistochemistry and available follow-up, were noted. Median age was 47.5 years (range 33-60 years). Interestingly, 7/14 cases (50 %) either had a family history of malignancy or a germline BRCA1 mutation. Diagnostic core biopsies (n = 12) showed IBC in 5, MGA-CA in 3, and only atypical MGA (AMGA) in 4. Nearly all MGA-CA were grade 3 (22/23), no special type (15/23), and TNBC (22/23). Typical and/or AMGA showed a transition to AMGA-like in-situ carcinoma to IBC (12/23) or merged directly with IBC (9/23). Both MGA and IBC showed mutant-type p53 expression in the majority (11/14). The median follow-up duration (n = 16) was 46 months (range 4-128 months). Patients receiving neoadjuvant chemotherapy showed a good response (4/5 cases). Local/metastatic tumor progression was noted in 7/16 cases (43.75 %), higher in those with family history/BRCA+ status than without (57.1 % vs 33.3 %). Our study represents the second-largest single institutional MGA-CA series to date. Mutant-type p53 overexpression is noted in both MGA and associated CA, reinforcing MGA as a likely precursor to high-grade TNBC-type IBC. Diagnosis is possible even on core biopsies. Family history/germline BRCA mutations are frequent and herald higher chances of progression, suggesting the need for genetic testing in MGA-CA.