- A large Israeli observational study of osteoporotic or osteopenic postmenopausal women fails to show that exposure to bisphosphonates protects against breast cancer onset.
Why this matters
- This observational study using 5 levels of exposure does not support 2 prior observational studies, but does support the negative results of prior randomized controlled trials.
- The evidence suggests that positive studies might reflect low estrogen rather than an antitumor effect of bisphosphonates.
- Historical prospective study (n=11,717) using databases of the Israeli Maccabi Healthcare Services (MHS).
- Exposure to bisphosphonates (alendronate or risedronate) among postmenopausal women with osteoporosis of osteopenia was stratified into quintiles of proportion of days covered (PDC) with bisphosphonates during the follow-up, which was a minimum of 5 years.
- Breast cancer incidence was obtained from the Israel National Tumor Registry.
- Funding: None.
- 173 incident breast cancers were seen over a total of 130,252 person-years of follow-up.
- Compared with PDC of 20% or lower (the lowest quintile of exposure), the adjusted HRs for breast cancer at higher quintiles were:
- PDC 21%-40%: HR, 0.816; P=.455.
- PDC 41%-60%: HR, 0.818; P=.420.
- PDC 61%-80%: HR, 0.727; P=.179.
- PDC 81%-100%: HR, 1.146; P=.504.
- Multiple comparisons.