Background

Liquid biopsies analyzing circulating tumor DNA (ctDNA) and circulating tumor cells (CTCs) enable minimally invasive monitoring and testing of lung cancer across different stages. Approximately 90% of patients succumb due to metastasis. However, identifying patients with early metastatic signatures remains extremely challenging. In addition, monitoring minimal residual disease (MRD) and identifying patients at risk of recurrence is highly important. While the prognostic role of CTCs in predicting survival has been established in several cancers, the combined role of CTCs and ctDNA in monitoring disease aggressiveness, treatment response, and therapeutic decision-making has not been extensively explored. In this study, we investigated the combined roles of ctDNA and CTCs in monitoring disease aggressiveness and metastasis in lung cancer patients.

Methods

A cohort of 265 late-stage lung cancer patients was retrospectively analyzed for the co-occurrence of the dual biomarkers ctDNA and CTCs. The results were correlated in a quadrant-based model to assess clinical disease states derived from PET scans and histopathological examination (HPE) findings. Next-generation sequencing (NGS) was performed using the OncoMonitor dual biomarker assay, which includes CTC enumeration with PD-L1 expression analysis. CTC counts were determined using the OncoDiscover Liquid Biopsy Test, approved by CDSCO-India, from 1.5 mL of blood.

Results

CTC distribution ranged from 1 to 8 cells, with a mean value of 1.22. Among the patients, 75.47% (n = 200) were CTC-positive, and among these, 91.50% (n = 183) exhibited PD-L1 expression on their CTCs, with a mean PD-L1–positive CTC value of 0.99. Both biomarkers were positive (ctDNA⁺/CTC⁺) in 135 patients (50.94%). Only 19 patients (7.17%) were negative for both biomarkers (ctDNA⁻/CTC⁻). Additionally, 43 patients (16.23%) were ctDNA⁺/CTC⁻, while 68 patients (25.66%) were ctDNA⁻/CTC⁺. The ctDNA⁺/CTC⁻ cohort exhibited the highest metastatic rate at 62.8%, followed by the ctDNA⁺/CTC⁺ group at 57.0%. The ctDNA-positive cohort showed the highest proportion of progressive disease (20.2% and 18.6% in CTC⁺ and CTC⁻ subgroups, respectively). Mutations in EGFR, TP53, and KRAS were observed in 62.64% (166/265) of patients. Stable disease was observed in 29.4% of patients when both biomarkers were absent (ctDNA⁻/CTC⁻).

Conclusions

Overall, the ctDNA-positive cohort demonstrated higher rates of MRD, disease progression, and metastasis, with no cases of stable disease. The combined quadrant analysis of CTC-PD-L1 cells and ctDNA provides a non-invasive approach for monitoring disease progression, treatment response, complete remission, and early metastatic detection in lung cancer patients.