Expression of Programmed Death-Ligand 1 and Programmed Death-1 in Patients with Extramammary Paget's Disease

Extramammary Paget's disease (EMPD) is a rare skin cancer and sometimes has fatal prognosis. For progressive cases, therapeutic options are limited. In recent years, treatment with an anti-programmed death-1 (PD-1) antibody has improved the prognosis of various malignancies. In addition, correlations between PD-ligand 1 (PD-L1) expression in tumor cells and favorable responses to anti-PD-1 therapy have been reported for several cancers. There have been a few case series of analysis of PD-L1 expression in patients with EMPD.

The purpose of this study was to investigate the relationship between the EMPD and PD-L1/PD-1 expression in Japanese EMPD patients.

We investigated 39 patients with EMPD by immunohistochemical staining of PD-L1 and PD-1. We counted the number of tumor cells that were positive for PD-L1 and the number of tumor-infiltrating mononuclear cells (TIMCs) that were positive for PD-L1 and PD-1. We also analyzed correlations between the expression of PD-L1 and PD-1 in EMPD and patients' characteristics.

We found that none of the Paget's cells expressed PD-L1. All of the specimens contained TIMCs, and some of the TIMCs expressed PD-L1 and PD-1. However, there was no correlation between the expression of PD-L1/PD-1 in TIMCs and patients' characteristics.

Although tumor cells did not express PD-L1 and the expression of PD-L1/PD-1 in TIMCs did not correlate with patients' characteristics, future clinical studies should be carried out to explore another immune escape pathway in EMPD.