Popular antidepressants taken with tamoxifen can increase the risk of breast cancer recurrence

A new study found that taking tamoxifen with certain antidepressants more than doubled the risk of breast cancer recurrence in women taking both medications. The antidepressants inhibit an enzyme, CYP2D6, which helps tamoxifen work effectively.

The study was conducted by researchers from Medco and the Indiana University School of Medicine and presented Saturday at the American Society of Clinical Oncology (ASCO) meeting in Orlando.

Approximately 500,000 U.S. women take tamoxifen, a medicine that blocks the effects of estrogen in breast tissue. Estrogen can make certain types of breast cancer (hormone-receptor-positive breast cancers) grow. About 30 percent of women taking tamoxifen also are taking an antidepressant to treat depression and/or to ease hot flashes, a common side effect of tamoxifen. "With more than 100,000 women potentially affected, these data represent a significant health finding," asserts Dr. Marisa Weiss, president and founder of Breastcancer.org and a breast oncologist at Lankenau Hospital in the Philadelphia area.

Preliminary, limited information from another study conducted by researchers from the Netherlands appears to offer conflicting results. The Dutch study suggests taking tamoxifen with specific antidepressants doesn't affect breast cancer recurrence rates.

"We don't want to dismiss the findings of the Dutch study; however, from what we've learned, there were fewer women in the Dutch study taking antidepressants in combination with tamoxifen, and it appears that they were taken together for a shorter period of time," says Dr. Weiss. "Regardless, there is considerable evidence in the Medco/Indiana University study, as well as in other smaller studies conducted during the past few years, to give physicians and patients reason to question using certain antidepressants (and other types of medications that might block the CYP2D6 enzyme) together with tamoxifen."

Tamoxifen has been used to successfully treat millions of women diagnosed with hormone-receptor-positive breast cancer. It can reduce the risk of cancer recurrence by about 50 percent.

"With the life-saving advantages of tamoxifen, it's imperative that women taking it derive the greatest benefit they can," says Dr. Weiss. "Women make a daily commitment to tamoxifen and deserve to get the maximum benefit this medicine affords."

She pointed out that there are safe and effective alternatives to manage depression and hot flashes that doctors can offer patients taking tamoxifen. Weiss advises women who have taken tamoxifen along with an antidepressant in the past and those who currently are taking these medicines together to talk to their doctors. Anyone with questions also can find information at Breastcancer.org.

"Since tamoxifen is the cornerstone of care for hundreds of thousands of women across the globe, this study will likely raise a lot of questions about whether to continue to use tamoxifen or change treatments, as well as whether women who stopped taking tamoxifen should restart. These new data represent an important insight into maximizing the effectiveness of breast cancer treatment," says Dr. Weiss.