Longitudinal Assessment of Circulating Tumor Cells Expressing PD-L1 and Clusters in Esophageal Cancer Patients

Background

Carcinoma esophagus (CA esophagus) has a high recurrence rate and poor survival outcomes. Despite complete response (CR), a notable number of patients experience recurrence. Thus, pathological ‘no evidence of disease’ may not always indicate disease-free survival (DFS), particularly in the presence of occult systemic disease and micro-metastasis. Circulating tumor cells (CTCs) with PD-L1 overexpression may offer both prognostic and predictive value. Similar approaches, such as AR-V7 expression in the PROPHECY study, have demonstrated the potential of CTC-based biomarkers in predicting treatment outcomes in metastatic castration-resistant prostate cancer. Longitudinal CTC assessment may provide evidence of active clonal evolution, minimal cellular residual disease (MCRD), and therapy sequencing. We assessed the presence of PD-L1-overexpressing CTCs and CTC clusters in patients with CA esophagus.

Methods

We retrospectively assessed 110 patients with CA esophagus using peripheral 1.5 mL blood samples collected at baseline (BL) (n=86; 78.2%) and follow-ups (FU) (n=24; 21.8%). CTC enumeration and PD-L1 expression analysis were performed using the CDSCO-approved OncoDiscover® platform. CTCs were identified based on EpCAM⁺, CK18⁺, DAPI⁺, CD45⁻, and PD-L1⁺ markers using a fluorescence automated microscope. Mean CTC distributions were calculated across multiple time points and longitudinal means were compared between BL and FU.

Results

Among 110 patients, 83 (75.5%) were CTC-positive. PD-L1 expression was detected in 63 patients (57.3%), while CTC clusters were observed in 14 patients (12.7%). Most patients (89/110; 80.9%) were aged 51–80 years, with a mean age of 59.7 years, and 67.3% were male. At baseline, 65/86 (75.6%) patients were CTC-positive, with 47 (54.7%) showing PD-L1 overexpression. At follow-up, 18/24 (75%) patients remained CTC-positive, of whom 16 (66.7%) demonstrated PD-L1 positivity. The mean CTC count was 1.37 at BL and 1.20 at FU, with a combined mean of 1.32. The mean distribution of PD-L1-positive CTCs was 0.83 at baseline, 0.91 at follow-up, and 0.85 overall. CTC clusters increased at follow-up compared with baseline (0.25 vs. 0.12).

Conclusions

We longitudinally monitored and assessed PD-L1-expressing CTCs and CTC clusters in esophageal cancer patients at baseline and follow-up. PD-L1-positive CTCs may have potential as a predictive biomarker for treatment outcomes and the detection of occult minimal cellular residual disease.