Purpose <p>This study aims to explore the connection between rumination and posttraumatic growth (PTG) in cancer patients, while also investigating the underlying factors that may explain the mixed findings observed in prior research on this relationship.</p> Methods <p>The PRISMA method for evidence synthesis was adopted in the study. Studies published from inception through August 2024 that reported a correlation between PTG and rumination (intrusive rumination and deliberate rumination) among people with cancer were identified through systematic searches in nine databases, including PubMed, PsycINFO, Embase, etc. Stata 18.0 was used to analyze the overall effect size and conduct moderator analysis.</p> Results <p>Thirty-five studies comprising 8, 398 people with cancer and 70 effect sizes were identified. There was no significant relationship between people with cancer’s intrusive rumination and PTG, though factors like multiple cancers and disease stage played a notable role in influencing this relationship. A modest yet positive correlation emerged between deliberate rumination and PTG among those with cancer, with the stage of cancer acting as a key factor in shaping this association.</p> Conclusions <p>The study suggested that cancer patients with greater degrees of deliberate rumination have a higher likelihood of experiencing growth as a result of cancer. To determine whether the relationship between people with cancer’s rumination and PTG changes causally over time, future longitudinal studies should be conducted.</p>