The importance of the tumour microenvironment dynamics during the neoplastic transformation of breast epithelial tissue is increasingly being recognised and is considered as a hallmark of cancer.3,39,40 However, the effect of infiltrating lymphocytes in various malignancies including DCIS is controversial14–16,41–43 and the role of PD1 and PDL1 proteins in DCIS remains to be defined. Here, PDCD1 is linked to cancer.