Abstract
Background: Programmed cell death protein 1 (PD-1) is a protein on the surface of T and B cells that has a role in regulating the immune system's response. PD-1 expression levels have been associated with prognosis of malignancies. The previous reports of PD-1 staining for mycosis fungoides (MF), however, are somewhat conflicting. Additionally, there have not been thorough investigations of the PD-1 staining in different variants of MF.Methods: A retrospective study was performed to investigate PD-1 expression in folliculotropic MF and patch/plaque MF cases using immunohistochemistry. Immunohistochemistry staining with PD-1 was performed on a total of 24 cases of folliculotropic MF and 18 cases of patch/plaque stage MF. The percentage of tumor cells labeled with PD-1 and PD-1 intensity score on a scale of negative, weak, medium, or strong were recorded.
Results: Significant differences in PD-1 labeling between the Patch/plaque MF and the folliculotropic MF were found (p = 0.028). Patch/plaque MF showed higher percentage of PD-1 labeling in tumor cells (58.3%) compared with the folliculotropic MF (40.2%). Among folliculotropic MF cases, 13 out of 24 showed differential PD-1 expression between epidermal and dermal components, with preserved PD-1 staining in the epidermal component and loss of staining in the dermal component. Additionally, consistent with prior literature, tumor cells with large cell transformations showed significantly lower PD-1 labeling (p = 0.017).
Conclusion: In this study, we demonstrate a significant difference in PD-1 expression between folliculotropic and classic patch/plague MF as well as differential loss of PD-1 expression in the dermal components of folliculotropic MF. These findings underscore the potential significance of PD-1 as a prognostic factor in MF overall survival and suggest its relevance in guiding personalized treatment strategies. Further investigations with larger cohorts with survival data are warranted to validate these results and explore the therapeutic implications of PD-1 expression in MF.