PDCD1 and ductal breast carcinoma in situ: 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.