A total of 2,216 of 151,592 postmenopausal women enrolled in the initiative were taking either alendronate (89.7%) or etidronate (10.1%) at their entry into the program.
Rowan Chlebowski, MD, PhD, a Medical Oncologist at the Los Angeles Biomedical Research Institute at Harbor-University of California, said that Researchers found a mean 32% fewer breast cancers among women using bisphosphonates compared to women who did not.
Chlebowski presented the findings during the 32nd Annual CTRC-AACR San Antonio Breast Cancer Symposium.
The rate of invasive breast cancer was 4.38 per 1,000 person-years of follow-up for non-bisphosphate users compared to 3.29 per 1,000 person-years for bisphosphonate users.
“Oral bisphosphonate use may directly inhibit breast cancer incidents,” Chlebowski 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.”
Using the hip fracture risk score to control for bone mineral density between bisphosphonate users and non-users, the researchers observed 30% fewer estrogen receptor-positive cancers and 34% fewer entry receptor-negative cancers in bisphosphonate users.
About bisphosphonates
Bisphosphonates (also called diphosphonates) are a class of drugs that prevent the loss of bone mass, used to treat osteoporosis and similar diseases.
Bone has constant turnover, and is kept in balance (homeostasis) by osteoblasts creating bone and osteoclasts digesting bone. Bisphosphonates inhibit the digestion of bone by osteoclasts.
Osteoclasts also have constant turnover and normally destroy themselves by a process called cell suicide (apoptosis). Bisphosphonates encourage osteoclasts to undergo apoptosis.
The uses of bisphosphonates include the prevention and treatment of osteoporosis, osteitis deformans (“Paget’s disease of bone”), bone metastasis (with or without hypercalcaemia), multiple myeloma, primary hyperparathyroidism, osteogenesis imperfecta and other conditions that feature bone fragility
Reference:
Chlebowski R. Oral bisphosphonate and breast cancer: Prospective results from the Women’s Health Initiative. Paper #21 Presented at: 32nd Annual CTCR-AACR San Antonio Breast Cancer Symposium; Dec. 9-11, 2009. San Antonio, Texas.