Once DCIS treatments are completed, tamoxifen is often recommended, even though this too is controversial.
Taking tamoxifen has its risks and side effects. According to the American Cancer Society, it increases the risk of endometrial (uterine) cancer and blood clots, although for uterine cancer, only by 1.6% in the tamoxifen group, compared with 0.5% in the placebo group (with an even lower risk of developing a serious blood clot). A 2009 study by Dr. Li also showed that women who used tamoxifen for five or more years were about four times more likely to develop a more aggressive ER-negative tumor in their other breast. Common side effects of tamoxifen are menopausal-like hot flashes, night sweats, and vaginal dryness.
According to Dr. Susan Love: “Tamoxifen is not a mandatory treatment. It is a choice. To decide whether it is right for you, you need to weigh the risks versus the benefits.” To do this, a study’s relative risk numbers must always be compared to its absolute risk numbers. For instance, when a 2005 study known as P-1 reported that tamoxifen reduced invasive breast cancer recurrence by 42%, the absolute risk reduction merely went from 4.25% to 2.48%, an actual reduction of only 1.77%. Again in 1998, although the Breast Cancer Prevention Trial found that tamoxifen reduced the incidence of breast cancer in women with atypia by 86 percent, when broken down to absolute risk reduction, this number was less than 1%.
Please listen to this video clip by Dr. Pam Popper as she explains how the absolute and relative risk reduction statistics on tamoxifen can be presented in misleading ways.
Dr. Michael Lagios, an international DCIS expert and pathologist reports that the 2011 updates of two trials (NSABP-B24 and UK/ANZ) employing tamoxifen as an adjuvant agent in DCIS patients resulted in the following commentary by Warrick and Allred. They “conclude that tamoxifen is probably overused, and advocate more selective use. They particularly note that the major benefit would be seen in patients who are younger (pre-menopausal) with extensive high-grade disease and/or narrow margins, and clearly only those that are ER positive.”
On his website, Dr. Lagios states: “The clinical benefit of tamoxifen intervention based on the randomized trials is meager at best. There appears to be no benefit, at least in the UK/ANZ trial for tamoxifen among irradiated patients, and the benefits when claimed are very small.”
Taking tamoxifen is a personal choice. Evaluating its benefit should always be based on the study’s absolute risk reduction, not the relative risk reduction. Once known, you can then decide if the benefits outweigh the risks for you.