CA9 and ductal breast carcinoma in situ: To investigate the intra-tumor heterogeneity of tumor hypoxia and T-cell regulation in breast tumors, 99 whole-tumor sections stained with dual marker CA9/FOXP3 from cases clinically classified as pure DCIS (n = 30) or invasive carcinomas with synchronous DCIS (IDC/DCIS, n = 34) were included in this study (Table 1).