Magnitude of Effect: Breast cancer incidence is approximately 25% lower in women who have taken bisphosphonates for more than a year, although this difference might be attributable to the lower breast cancer risk that is associated with decreased bone density. In women who have had estrogen receptor-positive breast cancer, bisphosphonate use is associated with a 59% decrease in the development of contralateral breast cancer, compared with similar women without bisphosphonate treatment.
|Study Design: Case-control studies.|
| Internal Validity: Good.|
|External Validity: Good.|
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