Purpose <p>Cancer patients who have undergone curative treatment may retain chronic, low-grade inflammation, a condition known to promote carcinogenesis, and, thus, cancer recurrence. We aimed to investigate whether home-based online exercise training can mitigate chronic, low-grade inflammation of cancer patients after curative oncologic surgery.</p> Methods <p>We analyzed data sets from 145 patients with breast, prostate, or colorectal cancer after curative surgery in the randomized controlled multicenter CRBP-TS trial. The intervention group was instructed to exercise at least twice weekly via video presentations for 6&#xa0;months. The control group received no video presentations. We analyzed the modified Glasgow prognostic score (mGPS) and plasma levels of interleukin (IL)-1 beta, IL-2, IL-6, IL-10, IL-12p70, tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) at baseline, after 3&#xa0;months, and after 6&#xa0;months. Baseline values were compared to normative values of healthy populations. Mixed-effect models were applied for statistical analysis of intervention effects.</p> Results <p>We detected baseline elevations of IL-1 beta, IL-2, IL-6, IL-10, IL-12p70, TNF-alpha, and IFN-gamma compared to normative values of healthy individuals. All patients in each group except for one had an mGPS of 0 at baseline. None of the cytokines revealed any significant interaction effects. After 6&#xa0;months, all patients had an mGPS of 0.</p> Conclusion <p>Cancer patients may exhibit low-grade chronic inflammation after surgery. In this study, home-based online exercise training did not affect low-grade chronic inflammation. Future studies should further investigate the efficacy of home-based online exercise training considering adjunctive therapies, other exercise modalities, and cancer types.</p> Trial registration <p>DRKS-ID: DRKS00020499; Registered 17 March 2020.</p> <p><a href="https://drks.de/search/en/trial/DRKS00020499">https://drks.de/search/en/trial/DRKS00020499</a></p>