Abstract

Background

Overexpression of the dynamic protein PD-L1 on circulating tumor cells (CTCs) is a highly implicative biomarker that represents post–curative intent status, minimal residual disease (MRD), disease aggressiveness, therapeutic response, and metastatic progression. We evaluated the correlation among CTC detection, PD-L1 expression, and CTC clusters present in solid tumors, namely lung, breast, colorectal, ovarian, and prostate carcinomas. Longitudinal monitoring of CTCs remains a major focus after treatments, including surgical intervention with curative intent.

Methods

Retrospectively, we analyzed 328 cancer patients (male 163, female 165) across stages, consisting of a total of 383 samples with baseline and follow-ups (n = 55). Cancer types included lung (27.13%), colorectal cancer (21.95%), breast (9.75%), ovary (4.2%), prostate (3.9%), and others. CTCs and clusters were detected from 1.5 ml peripheral blood using the OncoDiscover platform approved by the Central Drugs Standard Control Organization of India. The platform contains a multifunctional magneto-nanosystem mediated by anti-epithelial cell adhesion molecule (EpCAM) antibody. CTCs were confirmed as EpCAM+ve, CK18+ve, DAPI+ve, and CD45–ve. PD-L1 expression on CTCs was detected based on the linear intensity gradients of fluorescence signals using image acquisition on an automated fluorescence microscope.

Results

Among the 383 samples with baseline and follow-ups, 69.45% of patients had CTCs ranging from 1–11. Approximately 77% of patients were above the age of 50. The total number of CTCs observed was ~649 with a mean distribution of ~1.69. CTCs with PD-L1 overexpression were observed in 55.35% of patients (n = 266). Higher CTC prevalence was observed in lung cancer (24.75%), followed by colorectal cancer (21.57%) and breast cancer (5.89%). CTC clusters were observed in 10.18% of patient samples. Notably, concurrent positivity for both CTCs and PD-L1 expression was most prevalent in lung cancer patients, suggesting a potential aggressive disease phenotype and therapeutic vulnerability.

Conclusions

The findings support the integrated use of CTCs and their PD-L1 expression as a composite biomarker strategy to stratify patients for targeted therapies, immunotherapeutic interventions, and longitudinal monitoring.