Regional Variation in Deescalated Therapy in Older Adults With Early-Stage Breast Cancer.

Importance: Although trial data support the omission of axillary surgery and radiation therapy (RT) in women aged 70 years or older with T1N0 hormone receptor-positive (HR+) breast cancer, potential overtreatment in older adults with frailty persists. Objective: To determine how much geospatial variation in locoregional therapy may be attributed to region vs patient factors. Design, Setting, and Participants: This retrospective cross-sectional study included women aged 70 years or older who were diagnosed with HR+/ERBB2-negative (ERBB2-) breast cancer from January 1, 2013, to December 31, 2017. Data came from Surveillance, Epidemiology, and End Results-Medicare. Hierarchical multivariable modeling was used to evaluate the variance in deescalated care attributable to 4 domains, ie, (1) random, (2) region (health service area [HSA]), (3) patient factors, and (4) unexplained. Patient factors included age, frailty (validated claims-based measure), Charlson Comorbidity Index (CCI), and socioeconomic status (Yost index). Analyses were performed from January to October 2023. Exposure: HSA. Main Outcomes and Measures: Deescalated care, defined as omission of axillary surgery, RT, or both. Standard therapy was defined as lumpectomy, axillary surgery, and RT or mastectomy with axillary surgery. Multivariable logistic regression was used to identify factors associated with deescalated care receipt. Results: Of 9173 patients (mean [SD] age, 76.5 [5.2] years), 2363 (25.8%) were aged 80 years or older, 705 (7.7%) had frailty, and 419 (4.6%) had a CCI of 2 or greater. While 4499 (49.1%) underwent standard therapy, 4674 (50.9%) underwent deescalated therapy (1193 [13.0%] of the population omitted axillary surgery and 4342 [55.5%] of patients undergoing lumpectomy omitted RT). Of the total variance, random variation explained 27.3%, region/HSA explained 35.3%, patient factors explained 2.8%, and 34.5% was unexplained. In adjusted models, frailty and increased age were associated with a higher likelihood of undergoing deescalated therapy (frailty: odds ratio [OR], 1.70; 95% CI, 1.43-2.02; age, by 1-year increment: OR, 1.10; 95% CI, 1.09-1.11), but CCI was not. Patients in rural areas compared with those in urban areas (OR, 0.82; 95% CI, 0.68-0.99) and Asian and Pacific Islander patients compared with non-Hispanic White patients (OR, 0.68; 95% CI, 0.54-0.85) had a lower likelihood of undergoing deescalated therapy. Conclusions and Relevance: In this retrospective cross-sectional study of women aged 70 years or older diagnosed with T1N0 HR+/ERBB2- breast cancer, region/HSA contributed more to the variation in deescalated therapy use than patient factors. Unexplained variation may be attributed to unmeasured characteristics, such as multidisciplinary environment and patient preference. Decision support efforts to address overtreatment should target regions with low rates of evidence-based deescalation.