PDCD1 and follicular lymphoma: In the tumor microenvironment in follicular lymphoma, several types of T cells, such as CD4+ TH1 cells, CD8+ CTLs, and Treg cells are present; hence, the apparent inconsistencies between the results might reflect the fact that immunohistochemical analysis was used to assess PD-1 expression, which consequently prevents the accurate determination of the relative T-cell subsets that are PD-1 positive.