Triple Negative Metaplastic Breast Carcinoma Presenting in the Background of Atypical Microglandular Adenosis with Candidacy for Atezolizumab Immunotherapy

Microglandular adenosis (MGA) is a lesion that can have an infiltrative pattern,be mass producingand are often challenging to distinguish from a well-differentiated carcinoma. The atypical form, known as atypical microglandular adenosis (AMGA), has increased nuclear irregularity, increased density of glands, higher cytologic atypia, prominent nucleoli and numerous apoptotic bodies. Importantly, research has found that microglandular adenosis (MGA) is a non-obligate precursor of triple negative carcinoma of the breast. Most triple negative breast cancers carry a poor prognosis secondary to a lack of therapeutic response. Here we report a case of metaplastic breast carcinoma with chondrosarcomatous differentiation arising from atypical microglandular adenosis. We compare the expression of PD-L1 (SP142), PD-L1 (SP263) and PD-1 (NAT105) as part of the diagnostic and therapeutic workup. The findings demonstrated that this patient could be a candidate for Atezolizumab, an immunotherapeutic associated with clinical response in triple negative breast cancer.