Treatment Restarting After Discontinuation of Adjuvant Hormone Therapy in Breast Cancer Patients.

Background: Over half of breast cancer patients discontinue their adjuvant hormone therapy, permanently or temporarily. We aimed to identify predictors of treatment restarting after discontinuation of adjuvant hormone therapy and to test the hypothesis that treatment restarting is associated with better breast cancer outcomes.

Methods: We conducted a population-based cohort study by linking data from the Stockholm-Gotland Breast Cancer Register, the Swedish Prescribed Drug Register, and a self-reported questionnaire. We followed women diagnosed with breast cancer (Stockholm, Sweden, 2005-2008) from their first prescription of tamoxifen or aromatase inhibitors through January 31, 2015, and categorized them as continuers (n = 1 607), restarters (n = 953), and nonrestarters (n = 511) of adjuvant hormone therapy. All statistical tests were two-sided.

Results: Factors that decrease the likelihood of treatment restarting included younger age (<50 years), higher Charlson Comorbidity Score (≥2), smaller tumor size (<20 mm), human epidermal growth factor receptor 2 negative, lymph node negative, family history of breast cancer negative, using hormone therapy, using symptom relieving drugs, and switching therapy between tamoxifen and aromatase inhibitors. Restarting adjuvant hormone therapy was statistically significantly associated with prolonged disease-free survival, with an adjusted hazard ratio of 0.61 (95% confidence interval = 0.43 to 0.87, P = .006) for restarters vs nonrestarters.

Conclusions: Our study provides-for the first time to our knowledge-evidence that restarting adjuvant hormone therapy is associated with better breast cancer outcomes. Clinicians now have further evidence to encourage patients to restart their treatment after discontinuation of adjuvant hormone therapy.