Outcomes of primary endocrine therapy in elderly women with stage I-III breast cancer: a SEER database analysis

Background Frail elderly women with nonmetastatic hormone receptor-positive breast cancer often receive primary endocrine therapy. Limited data are available on the outcomes associated with this population and treatment approach. Methods We selected patients with an initial primary diagnosis of stage I-III ER-positive breast cancer from 2001 to 2015 in Surveillance, Epidemiology, and End Results (SEER)-Medicare data. Patients were excluded if they received surgery, radiation, chemotherapy, or other targeted drug treatment including anti-HER2 agents. Two Cox proportional-hazards models were constructed to determine the predictors of breast cancer-specific survival and overall survival after a cancer diagnosis. Results A total of 552 patients were identified, with 82.1% of the patients being 80 years or older and 81.7% of patients being non-Hispanic White. PR positive (OR 1.77; 95% CI 1.09-2.85; p = 0.025) and tumor size larger than 50 mm (OR 1.99; 95% CI 1.05-3.75; p = 0.035) were associated with higher adherence to endocrine therapy. In the multivariable Cox analyses, patients who were adherent of endocrine therapy had significantly worse survival (HR 1.40; 95% CI 1.17-1.69; p < 0.001). The other two factors associated with worse survival were larger tumor size and more comorbidities. The competing risk model demonstrated no statistically significant difference between patients who were adherent to endocrine therapy and those who were not in terms of risk of dying from breast cancer. Conclusion In elderly women with localized ER-positive breast cancer, there were no statistically significant differences in breast cancer-specific or overall mortality between those who were adherent to endocrine therapy and those who were not.