Can bisphosphonates reduce the risk of postmenopausal breast cancer?

June 24, 2010

Study Design: Population-based case-control study in northern Israel
Study Eligibility: Cases were postmenopausal patients that received a breast cancer diagnosis since January 1, 2000 in any hospital in Israel and lived in a geographically defined area of northern Israel at the time of diagnosis.  Controls were postmenopausal insurees of Clalit Health Services, the largest health provider, identified from the same geographical area
Enrollment: 1,832 cases and 2,207 controls
Research Question:  Is there a potential for breast cancer prevention with bisphosphonates?

In the Breast cancer in Northern Israel Study, the investigators evaluated the association between the use of bisphosphonates and the risk of developing breast cancer in postmenopausal women.   The controls were matched by age, clinic, and ethnicity to the cases.  Bisphosphonate use was assessed in 4,039 postmenopausal cases and controls using pharmacy records.   

The overall study response rate was 72.9% of all eligible patients.  Among those who were located and contacted, 85.6% agreed to participate, 1.4% were unable due to medical or language difficulties, and 13.0% declined participation.  The use of bisphosphonate for 1 year was associated with a significant reduction in breast cancer risk.  This association was not  affected by age, family history, ethnicity, body mass index (BMI), participation in sports, fruit and vegetable consumption, age at first pregnancy, number of children, number of months of breast feeding, and the use of hormone replacement therapy and calcium.   

The study suggests a possible protective effect of bisphosphonates against breast cancer development.  But this finding may be a reflection of the known association of low bone density with lower risk of breast cancer.  Bone density data was not available, so the investigators could not address this question.  In addition, there were other limitations in the study.  Among the cases, there was a higher percentage rate of participation refusal compared to the controls, so participation bias was present.  Also, data on possible risk factors were collected retrospectively and could have introduced recall bias.  Therefore, the study results cannot be used to draw definitive conclusions regarding the use of bisphosphonates and preventing breast cancer.  Further studies and clinical trials will need to be carried out to confirm and validate this study’s findings.         
 

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