Attendees at the 40th annual meeting of the Association of Clinical Oncologists were updated on the serum estrogen receptor modulator (SERM) raloxifene and the aromatase inhibitor (AI) exemestane. Newest research findings were presented on the possible benefits they may provide for postmenopausal breast cancer risk reduction. SERMs are a class of drugs that can block the cell's ability to use estrogen to stimulate the development of breast cancer.
This class of anti-estrogens includes tamoxifen, which is currently used by thousands of postmenopausal women with estrogen-receptor positive cancer to prevent recurrence following completion of their chemotherapy.
The SERM raloxifene is currently used to prevent and treat postmenopausal osteoporosis. Studies have shown that its use also decreases the risk of invasive breast cancer. In a report from Cancer Institute Medical Group in Santa Monica, California, the use of raloxifene reduced the risk of invasive breast cancer for the years four through eight by 59 percent. These results continue to support prior results that showed a reduction in risk during the first four years of use.
The incidence of uterine cancer, a risk associated with tamoxifen use, did not increase with the long-term use of raloxifene. "This could be very significant for the group of post-menopausal women who are at risk for both osteoporosis and breast cancer," said Cheryl Perkins, M.D., senior clinical advisor for the Susan G. Komen Breast Cancer Foundation and a breast cancer survivor. "Additionally, it may offer an alternative to aromatase inhibitors, where the risk for osteoporosis is a side effect." In a second study presented today, researchers from The University of Bergen in Norway looked at the effects of exemestane, an AI, on bone loss in 147 postmenopausal women after one year of follow-up. Aromatase inhibitors block the body's ability to produce estrogen.
Estrogen stimulates the growth of breast cancer tumors. AIs have gained attention in recent years as a possible alternative to tamoxifen or as a therapy that can be taken after the suggested five-year limit for taking tamoxifen dosing has elapsed. Like tamoxifen, AIs may prevent the recurrence of breast cancer in postmenopausal women who have completed chemotherapy.
AIs are associated with increased bone loss, but this study of exemestane found that there was no significant difference in bone loss from the spine and some modest loss of bone from the hip compared to the control group. Fracture rates were similar in both groups during the one-year trial.
This information may provide researchers with information on which AI will offer the most therapeutic effect while minimizing serious side effects like osteoporosis. "We need to see longer term results, but finding effective drugs with the least degree of potential side effects for the patient will continue to be an important direction of research," said Perkins.