Introduction

The risk of recurrence in non-metastatic endometrial cancer (EC) within 2–3 years is significant, ranging from 6% to 21%. Lymph node involvement is a key determinant of outcome prediction in patients with operable EC. To improve prognostic accuracy, particularly in the context of curative-intent surgery and adjunct therapy regimens, biomarkers such as circulating tumor cells (CTCs) have not been extensively evaluated in EC. The presence of CTCs as an occult disease component in EC may represent minimal cellular residual disease (MCRD) and could play a role in the metastatic cascade and invasion to distant organs. In this study, we evaluated the distribution of CTCs, their PD-L1 overexpression, and the occurrence of CTC clusters in EC patients.

Methods

A total of 154 blood samples were retrospectively analyzed, including 133 baseline and 21 follow-up samples (1.5 mL each). CTCs were isolated using the CDSCO India–approved OncoDiscover® CTC Test, which employs immunomagnetic enrichment targeting epithelial cell adhesion molecule (EpCAM). CTCs were identified based on immunocytochemical staining as CK18⁺, DAPI⁺, and CD45⁻ cells with distinct morphological features. Fluorescence imaging was performed using a Zeiss Axio Observer 7 microscope, and signal intensities were quantified to assess associations with clinicopathological parameters. PD-L1 expression on CTCs was evaluated through fluorescence-based immunostaining and quantified accordingly. Statistical analyses summarized total CTC counts, PD-L1–positive CTCs, and the presence of CTC clusters.

Results

A total of 336 CTCs were detected in 116 patients (75.3%). PD-L1 overexpression on CTCs was observed in 52.6% of samples (81 out of 154). Across all 154 patient samples analyzed, the mean values were 1.54 for total CTCs, 0.14 for CTC clusters, and 1.23 for PD-L1–positive CTCs. Notably, 21 patients (13.6%) demonstrated the presence of CTC clusters, accounting for 121 of the 336 total CTCs, suggesting more aggressive disease behavior. The highest proportion of patients belonged to the 61–70-year age group (41.55%).

Conclusions

This study demonstrates a high prevalence of CTCs in the endometrial cancer population. The presence of CTCs, CTC clusters, and PD-L1–overexpressing CTCs indicates occult minimal residual disease, disease aggressiveness, and potential progression toward metastasis. PD-L1 expression on CTCs may have implications for immunotherapy decision-making, particularly in situations where tissue biopsy is unavailable.