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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