In order to determine whether sampling error contributes to variation in intratumoral T cell counts, we sectioned through and enumerated CD8+ T cells in 13 primary colorectal adenocarcinoma and 12 breast carcinoma (6 ductal adenocarcinoma, 6 medullary carcinoma) cases (1 FFPE block per case). Here, CD8A is linked to medullary thyroid gland carcinoma.