Background

Combined analysis of biomarkers such as circulating tumor DNA (ctDNA) and circulating tumor cells (CTCs) overexpressing tumorigenic proteins offers insight into evolving genotypic transitions from primary tumors that lead to metastasis in distant organs. We report the comparative distribution of CTCs and ctDNA genomic profiling in patients stratified as primary colorectal cancer (CRC) patients alone and those with metastasis progression in the liver, lung, and lymph nodes.

Methods

Retrospectively, we analyzed 218 patients with primary CRC (n = 153; male n = 93 and female n = 60). Metastasis was accounted for in 65 patients, namely liver (n = 27), lung (n = 8), and lymph nodes (n = 30). A total of 285 peripheral blood samples (218 baseline and 67 follow-up) were analyzed for the distribution of CTCs and ctDNA with driver mutations. CTCs expressing PD-L1 were evaluated using the CDSCO-approved OncoDiscover platform using 1.5 ml of blood. CTCs were enumerated based on EpCAM+, CK18+, DAPI+, and CD45– markers using a Zeiss automated fluorescence microscope. Further, the OncoIndx comprehensive NGS assay was performed using a 1080-gene panel.

Results

At baseline, 64.8% of primary CRC patients had ≥1 CTC (mean CTC distribution ~1.1), while 55.9% of patients had detectable ctDNA. In patients with metastasis (n = 65), the mean CTC distribution was 1.8. Higher CTC distribution was observed in liver metastasis (41.5%), lymph node involvement (46.2%), and lung metastasis (12.3%). A total of 71.7% of patients had detectable CTCs, among which 88.2% showed PD-L1 expression, while 61.3% of patients had detectable ctDNA. Concordance rates were 83.7% and 100% between the presence of CTCs and ctDNA in baseline and follow-up samples from patients with primary cancer, respectively. Furthermore, a strong correlation was observed between elevated CTC counts and the presence of ctDNA mutations in key oncogenes, including KRAS, EGFR, and BRAF.

Conclusions

Higher co-occurrence of ctDNA with CTCs at both baseline and follow-up highlights the need for monitoring disease progression and assessing treatment response. Thus, combined analysis of CTCs and ctDNA provides significant prognostic value in metastatic colorectal cancer.