Physician-level variation in axillary surgery in older adults with T1N0 hormone receptor-positive breast cancer: A retrospective population-based cohort study

Introduction: We sought to determine how considerations specific to older adults impact between- and within-surgeon variation in axillary surgery use in women >= 70 years with T1N0 HR+ breast cancer. Materials and Methods: Females >= 70 years with T1N0 HR+/HER2-negative breast cancer diagnosed from 2013 to 2015 in SEER-Medicare were identified and linked to the American Medical Association Masterfile. The outcome of interest was axillary surgery. Key patient-level variables included the Charlson Comorbidity Index (CCI) score, frailty (based on a claims-based frailty index score), and age (>= 75 vs <75). Multilevel mixed models with surgeon clusters were used to estimate the intracluster correlation coefficient (ICC) (between-surgeon variance), with 1-ICC representing within-surgeon variance. Results: Of the 4410 participants included, 6.1% had a CCI score of >= 3, 20.7% were frail, and 58.3% were >= 75 years; 86.1% underwent axillary surgery. No surgeon omitted axillary surgery in all patients, but 42.3% of surgeons performed axillary surgery in all patients. In the null model, 10.5% of the variance in the axillary evaluation was attributable to between-surgeon differences. After adjusting for CCI score, frailty, and age in mixed models, between-surgeon variance increased to 13.0%. Discussion: In this population, axillary surgery varies more within surgeons than between surgeons, suggesting that surgeons are not taking an "all-or-nothing" approach. Comorbidities, frailty, and age accounted for a small proportion of the variation, suggesting nuanced decision-making may include additional, unmeasured factors such as differences in surgeon-patient communication.