Evaluating DNA damage in peripheral blood lymphocytes: a promising biomarker for diagnosis, prognosis, and treatment monitoring in colorectal cancer

Colorectal cancer (CRC) remains a major health challenge due to its late-stage diagnosis and the variability in patient prognosis. This study explores the potential of DNA damage in peripheral blood lymphocytes (PBLs) as a biomarker for CRC, comparing it with standard clinical parameters. We assessed DNA strand breaks using the alkaline comet assay in 27 CRC patients at diagnosis and post-treatment, comparing these levels with 31 healthy controls. Patients received 5-fluorouracil (5-FU) -based chemotherapy (with irinotecan or oxaliplatin), radiotherapy, or combined chemoradiotherapy. At diagnosis (t0), DNA damage in PBLs was significantly higher in CRC compared to healthy controls (mean ± SD %DNA in tail: CRC 27.9 ± 14.0%; controls 6.5 ± 3.8%; p = 0.001), and independently of common confounding factors (sex, age, smoking, and alcohol consumption). Crucially, the prognostic signal came from baseline (t0): 6 of 27 patients relapsed/metastasised within 8-10 months, and high DNA damage basal levels was the only significant prognostic predictor (p = 0.0137), yielding an infinitely elevated Odds Ratio (95% CI: ≥2.203) and 100% sensitivity. In stark contrast, carcinoembryonic antigen (CEA) and cancer antigen 19-9 (CA 19-9) showed limited performance. At t0, among patients with available serum data (n = 23), most values were below clinical cut-offs: CEA 3 ng/mL (14/23, 61%); CA19-9, 37 U/mL (19/23, 83%). Prognostic sensitivities were 50.0% (CEA) and 16.7% (CA19-9). Post-treatment (t1) increases in DNA damage are pharmacodynamically expected with DNA-damaging therapy. t1 values were higher in patients who relapsed (p < 0.001), whereas the within-patient change (Δ = t1 - t0) was not associated with outcome (p = 0.148); these post-treatment findings are exploratory. Evaluating DNA damage in PBLs, therefore, offers a valuable non-invasive biomarker for early detection, treatment monitoring, and short-term risk stratification in CRC, warranting validation in larger, stage-balanced cohorts.