PD-1, PD-L1, and PD-L2 Immunoexpression in Mycosis Fungoides Biopsies

Mycosis fungoides (MF) is a cutaneous T-cell lymphoma that typically progresses slowly and has a favorable initial prognosis; however, the clinical course worsens in advanced stages. The aim of this study was to investigate the levels of programmed death-1 (PD-1), PD-L1, and PD-L2 immunoexpression in the biopsies of patients with MF. Paraffin blocks from biopsies of 82 patients diagnosed with MF between 2019 and 2025 were selected for this study. Early-phase (initial) and later-phase lesion groups, as well as CD4-positive and CD8-positive disease groups were formed based on histological findings. Immunohistochemical staining was performed for PD-1, PD-L1, and PD-L2. Positivity scores were generated for tumor cells, cells in the tumor microenvironment, and combined positivity scores. Immune scores were statistically compared across the lesion phase, CD4‑CD8 positivity status, age, and sex. Of the patients, 56 (68%) had later-phase lesions, 26 (32%) had early-phase lesions, 64 (78%) were CD4-positive, and 18 (22%) were CD8-positive. PD-1, PD-L1, and PD-L2 expression levels are higher in later-phase lesions than in early-phase lesions. The effect size was found to be small to moderate. CD4 or CD8 positivity, age, and sex did not affect PD-1, PD-L1, or PD-L2 levels. Immune checkpoint inhibitors could be beneficial in the management of MF, a disease that is difficult to treat in the advanced stages. Studies with larger patient series, in which evaluation can be performed alongside clinical staging, are needed.