Immunohistochemical profiling of PD-L1 expression in neuroendocrine carcinoma of the uterine cervix.

Introduction: Neuroendocrine carcinoma (NEC) of the uterine cervix is a rare and aggressive malignancy for which disease-specific treatment strategies remain limited. Although immune checkpoint inhibitors (ICIs) have demonstrated activity in several cancers, PD-L1 expression in cervical NEC remains insufficiently characterized. This study descriptively evaluated PD-L1 expression patterns in cervical NEC using the PD-L1 IHC 22C3 pharmDx assay. Methods: Six surgically resected cervical NEC specimens from Taiwanese women treated between 2010 and 2024 were retrospectively analyzed. PD-L1 expression was assessed using the PD-L1 IHC 22C3 pharmDx assay. TPS, CPS, and IC scores were evaluated descriptively; TC was also recorded but was numerically identical to TPS in all cases and is therefore reported jointly as TPS/TC. Thresholds of TPS/TC ≥1%, CPS ≥1, and IC ≥5% were used solely for exploratory analyses and were not interpreted as validated clinical cutoffs for cervical NEC. Results: Tumor-cell PD-L1 expression was uncommon, with TPS/TC ≥1% observed in one case (16.7%). CPS ≥1 and IC ≥5% were each observed in three of six cases (50%). PD-L1 staining was more frequently observed in tumor-infiltrating immune cells than in tumor cells. One case demonstrated dual-compartment staining, with CPS 25, TPS/TC 3%, and IC 30%. Discussion: In this small cohort, PD-L1 expression was heterogeneous. Tumor-cell positivity by TPS/TC was uncommon and largely limited to a single case, whereas PD-L1 staining was more frequently observed in immune cells. CPS and IC provided complementary descriptive information on PD-L1 distribution; however, their biological relevance and predictive value remain unvalidated in cervical NEC. Larger studies integrating molecular profiling, functional immune characterization, and clinical outcome data are needed to determine the potential clinical utility of PD-L1 assessment in this rare malignancy.