Abstract Background Cancer is one of the most expensive conditions to treat, which reinforces the need to identify strategies for lowering costs. The aim of this study was to examine how physical activity is associated with health care costs after a cancer diagnosis. Methods Participants with a history of cancer ( N = 12,268) were identified from the linked Cancer Prevention Study II and Medicare claims data set (1999–2017). Moderate‐ to vigorous‐intensity aerobic physical activity (MVPA) was reported before and after diagnosis, and categorized to be consistent with guidelines. Multivariable general linear models assessed the associations between prediagnostic MVPA and pre‐ to postdiagnostic MVPA trajectory groups with health care costs in the year after diagnosis and median annualized costs in 2017 US dollars. All models were stratified by cancer stage. Results Among cancer survivors (mean age, 76 years [SD, 5.7 years]; 45.9% women) diagnosed with in situ cancer (13%), those who were inactive (0 metabolic equivalent task hours per week [MET‐h/week]) before diagnosis had higher health care costs in the year after diagnosis compared to participants who met guidelines (7.5–<15 MET‐h/week; $22,734 [95% confidence interval (CI), $16,841–$28,626] inactive vs. $18,922 [95% CI, $13,491–$24,352] meeting guidelines; p = .026). Among survivors diagnosed with local‐stage disease (58%), the most active survivors incurred the lowest costs ($34,347 [95% CI, $31,072–$37,623] most active vs. $36,717 [95% CI, $33,142–$40,291] no MVPA; p = .077). Across all stages, survivors with low MVPA before and after diagnosis consistently had higher costs than survivors with low MVPA before and high MVPA after diagnosis (additional annual costs by stage: in situ, $3641; local, $2160; regional/distant, $7617). Conclusions Cancer survivorship guidelines describe the health benefits of MVPA; this study provides evidence of the potential economic benefits of MVPA.
