CD8A and digestive system cancer: Given these findings and the lack of published evidence documenting the extent of TIL heterogeneity in whole tumor sections or biopsies, we evaluated CD8+ T cell prevalence in step sections from breast and colon tumor blocks and simulated core biopsy samples to determine the variability of tumor-associated CD8+ T cell prevalence between levels within a block and between simulated core biopsies and whole tissue sections as well as block means.