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Accumulation of DNA damage is a critical feature of genomic instability, which is a hallmark of various cancers. The enzyme-modified comet assay is a recognized method to detect specific DNA lesions at the level of individual cells. In this cross-sectional investigation, we explore possible links between clinicopathological and treatment related factors, nutritional status, physical activity and function, and DNA damage in a cohort of colorectal cancer (CRC) patients with non-metastatic disease. Levels of DNA damage in peripheral mononuclear blood cells (PBMCs) assessed 2–9 months post-surgery, were compared across tumour stage (localized (stage I-II) vs. regional (stage III) disease), localization (colon vs. rectosigmoid/rectum cancer), and adjuvant chemotherapy usage, with the last dosage administrated 2–191 days prior to sampling. Associations between DNA damage and indicators of nutritional status, physical activity and function were also explored. In PBMCs, DNA base oxidation was higher in patients diagnosed with regional compared with localized tumours (P = 0.03), but no difference was seen for DNA strand breaks (P > 0.05). Number of days since last chemotherapy dosage was negatively associated with DNA base oxidation (P < 0.01), and patients recently receiving chemotherapy (<15 days before blood collection) had higher levels of DNA base oxidation than those not receiving chemotherapy (P = 0.03). In the chemotherapy group, higher fat mass (in kg and %) as well as lower physical activity were associated with greater DNA base oxidation (P < 0.05). In conclusion, DNA base oxidation measured with the enzyme-modified comet assay varies according to tumour and lifestyle related factors in CRC patients treated for non-metastatic disease. [Display omitted] • DNA base oxidation varies in non-metastatic colorectal cancer remission. • High levels potentially affect prognosis and the risk of long-term side effects. • Enzyme-modified comet assay serve as a valuable biomarker for DNA base oxidation. [ABSTRACT FROM AUTHOR]

DNA repair is essential to maintain genomic integrity and may affect colorectal cancer (CRC) patients' risk of secondary cancers, treatment efficiency, and susceptibility to various comorbidities. Bioactive compounds identified in plant foods have the potential to modulate DNA repair mechanisms, but there is limited evidence of how dietary factors may affect DNA repair activity in CRC patients in remission after surgery. The aim of this study was to investigate the effect of a 6-month personalized intensive dietary intervention on DNA repair activity in post-surgery CRC patients (stage I-III). The present study included patients from the randomized controlled trial CRC-NORDIET, enrolled 2–9 months after surgery. The intervention group received an intensive dietary intervention emphasizing a prudent diet with specific plant-based foods suggested to dampen inflammation and oxidative stress, while the control group received only standard care advice. The comet-based in vitro repair assay was applied to assess DNA repair activity, specifically base excision repair (BER), in peripheral blood mononuclear cells (PBMCs). Statistical analyses were conducted using gamma generalized linear mixed models (Gamma GLMM). A total of 138 CRC patients were included, 72 from the intervention group and 66 from the control group. The BER activity in the intervention group did not change significantly compared to the control group. Our findings revealed a substantial range in both inter- and intra-individual levels of BER. In conclusion, the results do not support an effect of dietary intervention on BER activity in post-surgery CRC patients during a 6-month intervention period. [Display omitted] • DNA repair is essential to maintain genomic integrity. • Prudent diet does not moderate base excision repair in colorectal cancer patients. • Base excision repair activity varies in non-metastatic colorectal cancer remission. • Comet-based in vitro repair assay serve as a valuable biomarker for DNA repair. [ABSTRACT FROM AUTHOR]