Medicare Accountable Care Organization Enrollment and Appropriateness of Cancer Screening.

Importance: Despite rapid diffusion of Accountable Care Organizations (ACOs), whether ACO enrollment results in observable changes in cancer screening remains unknown. Objective: To determine whether Medicare Shared Savings Program (MSSP) ACO enrollment changes the appropriateness of screening for breast, colorectal, and prostate cancers. Design, Setting, and Participants: For this population-based analysis of Medicare beneficiaries, we used Medicare data from 2007 through 2014 and evaluated changes in screening associated with ACO enrollment using differences-in-differences (DD) analyses. We then performed difference-in-difference-in-differences (DDD) analyses to determine whether observed changes in cancer screening associated with ACO enrollment were different across strata of appropriateness, defined using age (65-74 years vs ≥75 years) and predicted survival (top vs bottom quartile). Main Outcomes and Measures: Rates of breast, colorectal, and prostate cancer screening measured yearly as a proportion of eligible Medicare beneficiaries undergoing relevant screening services. Results: Among Medicare beneficiaries, comprising 39 218 652 person-years before MSSP enrollment and 17 252 345 person-years after MSSP enrollment, breast cancer screening declined among both ACO (42.7% precontract, 38.1% postcontract) and non-ACO (37.3% precontract, 34.1% postcontract) populations. The adjusted rate of decline (DD) in the ACO population exceeded the non-ACO population by 0.79% (P < .001). This decline was most pronounced among elderly women (-2.1%), with minimal observed change among younger women (-0.26%). Baseline colorectal cancer screening rates were lower than those for breast cancer among both ACO (10.1% precontract, 10.3% postcontract) and non-ACO (9.2% precontract, 9.1% postcontract) populations. We observed an adjusted 0.24% (P = .03) increase in screening associated with ACO enrollment, most pronounced among younger Medicare beneficiaries (0.36%). For breast and colorectal cancer, we observed statistically significant differences in estimates of effect between age strata, suggesting that the ACO effect on cancer screening is mediated by age (DDD for both P < .001). Prostate cancer screening declined among ACO (35.1% precontract, 28.5% postcontract) and non-ACO (31.2% precontract, 25.7% postcontract) populations. The adjusted rate of decline in the ACO population exceeded that of the non-ACO population by 1.2%. We observed no difference in estimate of effect between age strata, suggesting that the ACO-mediated changes in prostate cancer screening are similar among younger and elderly men. Results characterizing appropriateness with predicted survival mirrored those when stratified by age. Conclusions and Relevance: Medicare Shared Savings Program ACO enrollment is associated with more appropriate breast and colorectal screening, although the magnitude of the observed ACO effect is modest in the early ACO experience.