Bisphosphonate Use and Breast Cancer Risk among Women with Ductal Carcinoma In Situ.

Women with a history of ductal carcinoma in situ (DCIS) have an elevated risk of a subsequent invasive breast cancer, but there are few established potentially modifiable factors known to lower this risk. Bisphosphonates are a commonly used treatment for patients with osteoporosis and have been shown to lower risks of recurrence and mortality in patients with invasive breast cancer; however, their use has not previously been investigated within the context of DCIS. Utilizing a population-based nested case-control design, we compared 301 cases of women diagnosed with DCIS and a subsequent breast cancer and 587 individually matched controls (on age, DCIS diagnosis year, primary treatment, histology, grade, and disease-free survival time) who were diagnosed with DCIS but never a subsequent breast cancer. Information on recency and duration of bisphosphonate use was ascertained from patient interviews and medical record reviews. Current users of bisphosphonates had a reduced risk of developing an invasive breast cancer compared with never users [OR = 0.50; 95% confidence interval (CI): 0.26-0.99]. Users of bisphosphonates for ≥48 months had a similar reduction in risk (OR = 0.45; 95% CI, 0.24-1.06). This is the first study to document that bisphosphonate use is associated with a lower risk of subsequent invasive breast cancer among women with a history of DCIS. This finding is consistent with the protective effect of bisphosphonates observed in other breast cancer settings. If validated by others, bisphosphonates may be an effective risk-reducing approach with the potential added benefits of its positive impacts on bone health and fracture risk. SIGNIFICANCE: This study finds that bisphosphonate use among women with a history of DCIS is associated with lower risk of subsequent invasive breast cancer, providing a potential preventative approach for this high-risk population. ©2021 American Association for Cancer Research.