Evaluating the Long-Term Impact of a Cooperative Group Trial on Radiation Use and Adjuvant Endocrine Therapy Adherence Among Older Women.

BACKGROUND: Using long-term survival data from the C9343 trial as a temporal reference point, this study aimed to determine radiation therapy (RT) treatment trends for older patients with early-stage breast cancer. The study also examined rates of adherence to adjuvant endocrine therapy (AET). METHODS: The surveillance, epidemiology, and end results-medicare database was used to identify women with a diagnosis of breast cancer from 2007 through 2016. Bivariate associations were calculated to determine variable characteristics by time frame (group 1: 2007-2012 vs. group 2: 2013-2016). Multivariate logistic regression was used to estimate the effect of group on the RT use and AET adherence. The temporal rates for both RT and AET adherence over time were plotted. RESULTS: The final study cohort included 12,210 Medicare beneficiaries. Use of RT differed significantly between the groups, with a higher proportion omitting RT in the later period (25% of group 2 vs. 20% of group 1; p < 0.001). In both groups, after adjustment for covariates, the patients with RT omitted were statistically less likely to adhere to AET [group 1: odds ratio (OR), 0.74; p < 0.001 vs. group 2: OR, 0.66; p < 0.001]. CONCLUSION: This study, 15 years after publication of the of the C9343 trial results, showed minimal change in practice, with most older women receiving RT. Importantly, AET adherence was significantly lower in the non-RT group. For women who meet the criteria to have adjuvant RT omitted, nonadherence to AET could result in undertreatment of their breast cancer, and RT should not be considered overtreatment.