Relationship of the Breast Ductal Carcinoma In Situ Immune Microenvironment with Clinicopathological and Genetic Features

The immune microenvironment of breast ductal carcinoma (DCIS) has yet to be fully explored, and the relationship of immune cells to genetic features of DCIS is unknown. We quantified tumor associated lymphocytes (TIL) and evaluated PD-L1 protein levels by immunohistochemistry in a cohort of pure DCIS (138 and 79 cases, respectively), some of which had copy number ( = 55) and mutation data ( = 20). TILs were identified in the stroma surrounding DCIS (119/138, 86%) and present at a median TIL score of 5% (range, 0%-90%). Most DCIS were negative for tumor cell PD-L1 staining (89%), but 25% of cases were positive for immune cell staining. We observed that, as in invasive breast cancer, TILs and PD-L1 positivity were significantly greater in high-grade ( = 0.002/0.035), ER-negative ( = 0.02/0.02), and -amplified tumors ( < 0.001/0.048). Comedo necrosis was significantly positively associated with TILs ( < 0.0001) but not with PD-L1. The TILs score was significantly higher in cases with mutation ( = 0.03) but not with or mutation. In the cases with copy number data, both the fraction of the genome altered and the number of telomeric imbalances were significantly positively correlated with TILs (both < 0.001). This result strongly contrasted with invasive breast cancer data, where aneuploidy was not correlated to TIL levels. Although a small cohort, our data suggest a preliminary model by which the progression of DCIS to invasive carcinoma may involve an altered relationship of tumor copy number with the immune microenvironment, possibly by the immunoediting of the tumor. .