Oral bisphosphonates associated with reduced invasive breast cancer incidence

San Antonio Breast Cancer Symposium

Findings from a prospective analysis of the Women’s Health Initiative showed that women taking oral bisphosphonates for osteoporosis were less likely to develop invasive breast cancer.

A total of 2,216 of 151,592 postmenopausal women enrolled in the WHI were taking oral bisphosphonates at entry (89.7% alendronate; Fosamax, Merck and 10.1% etidronate).

Rowan Chlebowski, MD, PhD, medical oncologist at the Los Angeles Biomedical Research Institute at Harbor-University of California, Los Angeles Medical Center said researchers found a mean 32% fewer breast cancers among women using bisphosphonates compared with women who did not.

The rate of invasive breast cancer was 4.38 per 1,000 person-years of follow-up for non-bisphosphate users compared with 3.29 per 1,000 person-years for bisphosphonate users (HR=0.68; 95% CI, 0.52-0.95). Only 64 of the bisphosphonate users studied developed breast cancer.

Moreover, the researchers observed 30% fewer estrogen receptor-positive cancers and 34% fewer entry receptor-negative cancers in bisphosphonate users.

Chlebowski presented the findings during the 32nd Annual CTCR-AACR San Antonio Breast Cancer Symposium.

“The idea that bisphosphonates could reduce breast cancer incidence is very exciting because there are about 30 million prescriptions for these agents written annually in the United States targeting bone health, and more could easily be used to counteract both osteoporosis and breast cancer,” he said in a press release.

Findings of a report from a breast cancer trial that suggested intravenous zoledronic acid every six months resulted in fewer cancers in the other breast, prompted this analysis. To control for use of bisphosphonates in the WHI, researchers conducted BMD analysis or used a 10-item hip fracture predictive score to measure bone density.

One hypothesis for the effect of bisphosphonates on breast cancer is that the drugs discourage blood vessel formulation and “reduce angiogenesis and stimulate immune cells responsible for tumor cell surveillance as potential mediators,” Chlebowski said.

“Oral bisphosphonate use may directly inhibit breast cancer incidence,” he said. “There are ongoing randomized trials in an adjuvant setting looking at contralateral breast cancer and may, in a year or so, be able to provide confirmation for this observational cohort finding.” – by Jason Harris

Chlebowski R. #21. Presented at: the 32nd Annual CTCR-AACR San Antonio Breast Cancer Symposium; Dec. 9-11, 2009; San Antonio, Texas.

This study has very important implications for a large population of patients — women who are affected with two common diseases: osteoporosis and breast cancer. This cohort study indicates the possibility that a simple oral drug may be effective to prevent both of these common diseases. Future studies, including some that are ongoing, should be able to address some of these issues. The findings presented here need to be confirmed by prospective, randomized trials, but these results represent a step forward in our ability to prevent breast cancer and osteoporosis

- Theresa A. Guise, MD
Jerry W. and Peg S. Throgmartin Professor of Oncology

Division of Endocrinology at the Indiana University School of Medicine