Bone Abstracts

Background: Bisphosphonates (BP) are widely used in osteoporosis treatment. By inhibiting the mevalonate pathway, bisphosphonates may affect cell function and survival, including the viability of tumor cells. Recently, a protective effect of bisphosphonates on breast cancer risk has been suggested by several studies, which were unable to exclude the possibility of a confounder effect due to low cumulative exposure to estrogen in osteoporotic women vs controls.

Study objective: To assess the association between different levels of bisphosphonate exposure and breast cancer incidence in a cohort of osteoporotic post-menopausal women.

Study methods: This historical prospective study was conducted using the computerized databases of Maccabi Healthcare Services (MHS). Included in the study were cancer-free women aged 55–75 who started bisphosphonate therapy between 1998 and 2012. Bisphosphonate exposure was expressed in quintiles of proportion of days covered with BP during follow-up period (PDC). Cancer incidence was ascertained by the Israel National Tumor Registry.

Results: A total of 18,122 eligible MHS members were identified. 11,717 remained for analysis with 173 cases of breast cancer diagnosed during a total follow-up period of 130,252 person-years, the mean follow up time was 7.2 years. Baseline characteristics of the study population are presented in Table 1. Compared to women with a PDC with bisphosphonates of 20% or lower, the hazard ratio for breast cancer were HR=0.95 95%CI (0.55–1.62), HR=0.74 95%CI (0.43–1.25), HR=0.82 95%CI (0.50–1.32) and HR=1.32 95%CI (0.86–2.02) among women with 20–40%, 40–60%, 60–80%, and 80% or higher respectively, adjusted for age, BMI, SES, smoking status, HRT use, mammograms, physician visits, and DXA scans (Table 2).

Conclusions: In the present study, we did not find any significant negative association between persistence with bisphosphonates and risk of breast cancer.