Clinicopathological assessment of PD-1/PD-L1 immune checkpoint expression in desmoid tumors

The details of immune molecules' expression in desmoid tumors (DTs) remain unclear. This study aimed to determine the expression status of the programmed death-1/programmed death ligand 1 (PD1/PD-L1) immune checkpoint mechanism in DTs. The study included patients with DTs (n=9) treated at our institution between April 2006 and December 2012. Immunostaining for CD4, CD8, PD-1, PD-L1, interleukin-2 (IL-2), and interferon-gamma (IFN-γ) was performed on pathological specimens harvested during the biopsy. The positivity rate of each immune component was calculated as the number of positive cells/total cells. The positivity rate was quantified and correlations between the positivity rates of each immune molecule were also investigated. Immune molecules other than PD-1 were stained in tumor cells and intra-tumor infiltrating lymphocytes. The mean ± SD expression rates of β-catenin, CD4, CD8, PD-1, PD-L1, IL-2, and IFN-ɤ were 43.9±18.9, 14.6±6.80, 0.75±4.70, 0±0, 5.1±6.73, 8.75±6.38, and 7.03±12.1, respectively. The correlation between β-catenin and CD4 was positively moderate (r=0.49); β-catenin and PD-L1, positively weak (r=0.25); CD4 and PD-L1, positively medium (r=0.36); CD8 and IL-2, positively medium (r=0.38); CD8 and IFN-ɤ, positively weak (r=0.28); and IL-2 and IFN-ɤ, positively medium (r=0.36). Our findings suggest that PD-L1-centered immune checkpoint mechanisms may be involved in the tumor microenvironment of DTs.