Tamoxifen: Causing Breast Cancer?
A new study shows that the “wonder drug” for treating breast cancer, tamoxifen, might cause a rare and aggressive form of breast cancer. However, this does not mean that breast cancer patients should stop using tamoxifen as soon as they read the published research.
Christopher Li, PhD and an associate member of the Fred Hutchison Cancer Research Center in Seattle, conducted a research examining tamoxifen’s effect on women who developed breast cancer in their other breast, almost six months from when they were first diagnosed.
Before examining the research, one must first understand the two types of breast cancer. ER positive or estrogen receptor positive is the most common type of breast cancer, which grows when exposed to estrogen. Tamoxifen and other hormone therapies are used to stop the ER-positive breast cancer cells from dividing. While, the ER negative breast cancers are uncommon and extremely aggressive when compared to ER positive breast cancers. These cancers are not treated with tamoxifen or other estrogen related drugs, since ER-negative breast cancers are not sensitive to estrogen.
Li’s team researched data on a group of 1,100 Seattle women between the ages of 40-79 who were treated for ER-positive breast cancer. These women were treated for the cancer between 1990 and 2005. Out of the 1,100 women, 367 of them developed breast cancer in their other breast almost six months from when they were first diagnosed.
Through careful interviews and examination of medical records and usage of tamoxifen or other hormone therapies (how much was used and how often the drugs were used), the team came to a surprising conclusion.
Compared to women who never used tamoxifen, women who did were 60% less likely to develop an ER-positive cancer in the other breast.
However, women who used tamoxifen for a time period of five years or longer were four times more prone to developing ER-negative breast cancer in their other breast, compared to women who never used tamoxifen or other hormone therapy.
One must keep in mind that tamoxifen’s link to ER-negative breast cancer risk was found in those who used the drug for five years or more.
Patients should not stop using tamoxifen because of this finding, as its benefits outweigh the risk of ever developing a rare ER-negative breast cancer.
Molecular Structure for Tamoxifen
“We don’t think that it overall changes the risk-benefit equation, in that women who are eligible to take this drug probably should still take it because of its proven benefit,” Li said.
Just like all treatments, tamoxifen has its risks and benefits. Tamoxifen is also know to increase the risk of a stroke of endometrial cancer. Li does not believe that the dosage requirements should be changed because in the end, the benefits still win out.
“The randomized trials looking at tamoxifen have very convincingly shown that full benefit of the drug is only obtained when it’s used for five years,” Li says. “I don’t think they should change the recommendation that women should use it for the full five years.”
Vogel from the American Cancer Society is worried that people might acquire the wrong impression regarding the study. Vogel also notes that most women do not take tamoxifen for more than five years.
He clearly states, “”Certainly none of the data has suggested that we stop using tamoxifen or change the way we apply it. … The net benefit for tamoxifen is huge.”
In the future, Li’s team hopes to understand the exact link between ER-negative breast cancer risk and tamoxifen, especially how tamoxifen raises the risk.
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