A new anti-estrogen agent called fulvestrant appears to produce a longer duration of response than currently used anti-estrogens, according to recent results presented at the 23rd Annual San Antonio Breast Cancer Symposium.
Breast cancer is a common malignancy, with an estimated 200,000 new cases each year in the United States. Estrogen receptor-positive breast cancer is a type of cancer that has an overabundance of specific proteins, called estrogen receptors, to which estrogen can bind. This binding facilitates cellular replication and growth. Currently, many women with estrogen receptor-positive breast cancer are treated with drugs that either inhibit estrogen synthesis in the body or block estrogen from entering into the cancer cell.
Fulvestrant is a new anti-estrogen agent that has recently completed early phase clinical trials. Fulvestrant binds to estrogen receptors present in cancer cells and achieves its anti-estrogen effects through two separate mechanisms. First, when fulvestrant binds to the receptors, estrogen is crowded out and is no longer able to bind to these receptors. Second, fulvestrant degrades the estrogen receptors to which it is bound. Both of these mechanisms prevent cancer cells from accessing sufficient amounts of estrogen needed for growth and replication.
A recent clinical trial was performed directly comparing fulvestrant to anastrozole, a recently approved anti-estrogen (aromatase inhibitor) that lowers estrogen levels in the blood. In this trial, 400 postmenopausal women had early or advanced breast cancer and all had a cancer recurrence following previous hormonal therapy. The results indicated that 42% of patients receiving fulvestrant achieved an anti-cancer response, compared with 36.1% of patients receiving anastrozole. The average anti-cancer response for patients receiving fulvestrant was 19.3 months, compared to only 10.5 months for patients receiving anastrozole. Side effects of fulvestrant were comparable to those of anastrozole.
These results suggest that fulvestrant may produce a significant benefit for women with estrogen receptor-positive breast cancer over current standard therapies, particularly regarding the duration of response. Future clinical trials will further assess the efficacy and clinical potential of fulvestrant in early and late stage breast cancer patients. The combination of fulvestrant and other anti-aromatase agents is also warranted in future clinical trials. Patients with estrogen receptor-positive breast cancer may wish to speak with their physician about the risks and benefits of participating in a clinical trial further evaluating fulvestrant or other promising therapies. Two sources of ongoing information about clinical trials include comprehensive, easy-to-use listing services provided by the National Cancer Institute (cancer.gov) and eCancerTrials.com. eCancerTrials.com also provides personalized clinical trial searches on behalf of patients. (Proceedings from the 23rdAnnual San Antonio Breast Cancer Symposium, San Antonio, TX, December, 2000)
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