Initiation and Completion of Hormone Therapy in Older Women With Early-Stage Breast Cancer.

[PURPOSE] Clinical trials suggest that adjuvant radiation therapy (RT) may be omitted in women aged ≥65 years with early-stage, hormone-receptor-positive breast cancer, provided completion of 5 years of hormone therapy. However, at the time of RT consult, it is often unknown whether the patient will start hormone therapy or will start but not complete 5 years of therapy, either of which, if known in advance, would alter RT recommendations. We studied a cohort of patients who would have been eligible for RT omission to examine factors associated with declining or discontinuing hormone therapy.

[METHODS AND MATERIALS] Using a prospectively maintained institutional database, we identified patients aged ≥65 years who underwent surgery from 2010 to 2017 with stage I hormone-receptor-positive breast cancer. Patients were classified as having osteopenia or osteoporosis based on the lowest T-score on dual-energy x-ray absorptiometry. Missing data were replaced using multiple imputation. Recurrence and survival statistics were calculated using Kaplan-Meier analysis. Univariate and multivariate logistic regression analyses were used to assess factors associated with not starting or discontinuing hormone therapy.

[RESULTS] We identified 590 eligible patients. Of these, 453 (76.8%) started hormone therapy. Patients who did not start hormone therapy were older (mean age, 77.02 vs 72.46 years; P < .001), had a lower body mass index (mean, 25.36 vs 26.78 kg/m; P = .008), had lower dual-energy x-ray absorptiometry scores (mean score, -1.92 vs -1.58; P = .056), and were less likely to undergo axillary surgery (64.2% vs 86.8%; P < .001). Of the 453 patients who started hormone therapy, 315 (69.5%) completed at least 5 years of therapy. Discontinuation of hormone therapy was associated with older age (hazard ratio [HR], 1.082; 95% CI, 1.033-1.133; P = .001), not undergoing axillary surgery (HR, 0.365; 95% CI, 0.146-0.915; P = .032), and smoking (HR, 1.636; 95% CI, 1.001-2.676; P = .05). Patients who were single or never married were less likely to discontinue hormone therapy (HR, 0.281; 95% CI, 0.096-0.821; P = .020). Patients who completed 5 years of hormone therapy had significantly better local recurrence-free survival (96.8%) than those who stopped early (87.7%; P = .01) or did not start hormone therapy (88.7%; P < .001).

[CONCLUSIONS] Older age, osteopenia, and lower body mass index were associated with not starting hormone therapy, while older age, marital status, axillary surgery, and smoking history predicted discontinuation of hormone therapy. These factors may guide discussions regarding the omission of adjuvant RT.