BackgroundAlthough functional outcomes are important in surgery for elderly patients, the long-term functional prognosis following oncologic surgery is unclear. We retrospectively investigated the long-term, functional and survival prognosis following major oncologic surgery according to age among elderly patients.MethodsWe used a Japanese administrative database to identify 11,896 patients aged ≥ 65 years who underwent major oncological surgery between June 2014 and February 2019. We investigated the association between age at surgery and the postoperative incidence of bedridden status and mortality. Using the Fine–Gray model and restricted cubic spline functions, we conducted a multivariable, survival analysis with adjustments for patient background characteristics and treatment courses to estimate hazard ratios for the outcomes.ResultsDuring a median follow-up of 588 (interquartile range, 267–997) days, 657 patients (5.5%) became bedridden and 1540 (13%) died. Patients aged ≥ 70 years had a significantly higher incidence of being bedridden than those aged 65–69 years; the subdistribution hazard ratios of the age groups of 70–74, 75–79, 80–84, and ≥ 85 years were 3.20 (95% confidence interval [CI], 1.53–6.71), 3.86 (95% CI 1.89–7.89), 6.26 (95% CI 3.06–12.8), and 8.60 (95% CI 4.19–17.7), respectively. Restricted cubic spline analysis demonstrated an increase in the incidence of bedridden status in patients aged ≥ 65 years, whereas mortality increased in patients aged ≥ 75 years.ConclusionsThis large-scale, observational study revealed that older age at oncological surgery was associated with poorer functional outcomes and higher mortality among patients aged ≥ 65 years.Supplementary InformationThe online version contains supplementary material available at 10.1245/s10434-023-13566-5.