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Weighing the risks and benefits of tamoxifen
Family Physician, North York, Ont.
I read with interest Eric Wooltorton's article on tamoxifen for breast can-cer prevention, which directly fol-lowed a summary of the Women's Health Initiative (WHI) study on hormone replacement therapy (HRT). The latter study was stopped early because the prespecified upper boundary for risk of breast cancer in the HRT group had been exceeded. To paraphrase Table 1 in Wooltorton's article, it appears that, per 10 000 woman-years, tamoxifen was associated with 15 more cases of endometrial adenocarcinoma, 2 more cases of uterine sarcoma, 4 more cases of stroke and 5 more cases of pulmonary embolism (relative to placebo), for a total of 26 additional events or a 1.3% absolute risk increase over the 5-year period of the National Surgical Adjuvant Breast and Bowel Project (NSABBP). Tamoxifen was associated with fewer cardiovascular problems than reported for HRT in the WHI study,2 but HRT did not cause any increase in endometrial cancer.
In the NSABP, the relative risk reduction for breast cancer among high-risk women who received tamoxifen was 49%. Perhaps the Gail model for identifying women at high risk of breast cancer could be modified to incorporate the known risks associated with tamoxifen, adjusted according to the patient's clinical characteristics, such as age, ethnic background and smoking status, to arrive at a net risk-to-benefit ratio. Without such a tool, it is difficult to get an accurate estimate of risk in clinical practice. A workshop has been held to quantify those risks, and the next step would be to incorporate the findings into a tool for hand-held or personal computers. A woman's decision to take tamoxifen would still depend on the values she places on different outcomes, such as stroke or breast cancer, but such a tool might help to estimate the risk–benefit ratio for her individual case.
References
- Wooltorton E. Tamoxifen for breast cancer prevention: safety warning. CMAJ 2002;167(4):378-9.
[Free Full Text] - Farquhar D. Postmenopausal hormone replacement therapy for chronic disease prevention: results from the Women's Health Initiative trial. CMAJ 2002;167(4):377-8.
[Free Full Text] - Fisher B, Costantino JP, Wickerham DL, Redmond CK, Kavanah M, Cronin WM, et al. Tamoxifen for prevention of breast cancer: report of the National Surgical Adjuvant Breast and Bowel Project P-1 Study. J Natl Cancer Inst 1998; 90:1371-88.
[Abstract/Free Full Text] - Gail MH, Costantino JP, Bryant J, Croyle R, Freedman L, Helzlsouer K, et al. Weighing the risks and benefits of tamoxifen treatment for preventing breast cancer. J Natl Cancer Inst 1999; 91:1829-46.
[Abstract/Free Full Text]
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