Tamoxifen, Raloxifene, and Arimidex: The Anti-Oestrogens
Tamoxifen, the market leader, is potentially effective only for patients with oestrogen-positive breast cancer. It also does not appear to be effective when the cancer has spread to the lymph nodes. Trials have shown that, with oestrogen-positive breast cancer, the longer a woman takes tamoxifen, the more she reduces her risk of a recurrence. Reviews typically report that 10% more women survive longer than ten years when they take tamoxifen for five years. However, these reviews also indicate that tamoxifen significantly increases the incidence of endometrial cancer – quadrupling it after those same five years of use. This is because tamoxifen causes the uterus to quickly thicken in virtually all test subjects, doubling their risk of endometrial cancer in the first year or two of use. Because the drug has anti-oestrogenic properties in some parts of the body and potent oestrogenic effects on others, it is known, along with raloxifene, as a selective oestrogen receptor modulator.
Other side effects of tamoxifen include a tripling of the risk for potentially fatal blood clots in the lungs, increased risk of stroke, blindness and liver dysfunction. In consideration of these potential problems, tamoxifen’s overall reduction in risk of mortality is considerably less than 10%.
The National Cancer Institute (NCI) admits that tamoxifen is indicated for preventive use only in women with increased risk of breast cancer, as determined primarily by family history. NCI estimates that only about 0.3% of women age 39 or younger would be candidates for tamoxifen treatment, yet it used to be common practice to put most women with breast cancer on the medication.
Raloxifene is the major rival for tamoxifen. It hasn’t been so extensively studied in long-term trials, but the general consensus is that it reduces recurrence in oestrogen-positive breast cancer only slightly better than tamoxifen, but with less risk for endometrial cancer and no real difference in risk for stroke or cardiovascular problems. Some have claimed that raloxifene might reduce cardiovascular risk because, like tamoxifen, it appears to lower LDL (bad) cholesterol and raise HDL (good) cholesterol. But a recent trial, which studied the effects of raloxifene in women who had a history of heart disease or who were at high risk for heart disease, showed that after more than five years of follow-up, participants experienced no real improvement in heart problems.  ......
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