Evaluation of circulating tumor cells expressing PD-L1 and CTC clusters at baseline and follow
ups in triple-negative breast cancer

Introduction: 

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype characterized by a high risk of recurrence and metastasis. Assessment of circulating tumor cells (CTCs), along with evaluation of PD-L1 expression and CTC clusters, provides prognostic, minimal cellular residual disease (MCRD), and predictive information. The duration of longitudinal CTC monitoring has not been established. This study evaluates the implications of detecting CTC burden, PD-L1 expression, and CTC clusters in TNBC patients at baseline and during follow-up for improved clinical outcomes.

Methods: 

This retrospective observational study analyzed 180 peripheral blood samples from patients with TNBC, including 141 baseline (BL) and 39 longitudinal follow-up (FU) samples. Peripheral whole blood (1.5 mL) was processed using the CDSCO-approved OncoDiscover liquid biopsy platform, which employs antibody-mediated immunomagnetic enrichment and automated fluorescence microscopy to identify EpCAM⁺/CK18⁺/DAPI⁺/CD45⁻ CTCs. CTC positivity was defined as ≥1 confirmed CTC. Descriptive statistics were used to evaluate CTC burden, PD-L1-positive CTCs, and CTC clusters across BL and FU cohorts and age groups.

Results: 

CTCs were detected in 114/180 (63.3%) patients, while 66 (36.7%) were CTC-negative. PD-L1-positive CTCs were identified in 62/114 (54.4%) CTC-positive patients (34.4% of the overall cohort), and CTC clusters were detected in 17/180 (9.4%) patients. The overall mean CTC count was 0.91, with higher values observed in FU than BL samples (1.18 vs. 0.81). Mean CTC cluster counts were also marginally higher in FU samples (0.10 vs. 0.09). Most CTC-positive patients harbored a single CTC (77/180, 42.8%), followed by two (14.4%), three (5.0%), and four (1.1%) CTCs. Patients aged 20–30 years demonstrated the highest mean CTC count (1.83), whereas those aged 71–80 years had the lowest mean CTC count (0.50).

Conclusion:

The OncoDiscover platform detected CTCs in nearly two-thirds of patients with TNBC and demonstrated that more than half of CTC-positive patients expressed PD-L1. Simultaneous assessment of CTC enumeration, PD-L1 expression, and CTC clusters represents a promising minimally invasive strategy for longitudinal disease monitoring and biomarker-guided management in TNBC. Monitoring changes in CTCs and the duration of longitudinal MCRD from baseline remains critical, although this is not yet well established.