The results of a new study suggest that side effects of tamoxifen, a breast cancer drug, can lead to decreased cognitive abilities and memory loss.
Women who took tamoxifen for a year or more were found to score lower on verbal memory and executive functioning tests, according to researchers at the Netherlands Cancer Institute in Amsterdam. Their results were published this month in the online version of the Journal of Clinical Oncology.
Tamoxifen was first approved by the FDA in 1971 for the treatment of breast cancer. Originally developed by AstraZeneca under the brand name Nolvadex, it is now sold under a variety of brand names, including Istubal and Valodex, and is also sold as a generic. Tamoxifen works by inhibiting the development of estrogen, which is believed to stimulate the spread of breast cancer. As of 2004, it was the largest selling hormone-based breast cancer treatment drug in the world.
Dutch researchers, funded by Pfizer, tested 299 women, including 80 women prescribed tamoxifen and 99 women taking Pfizer’s competing Aromasin (exemestane). They found that tamoxifen users had a statistically significant drop in verbal memory and executive functioning skills when compared to healthy control groups. Aromasin users showed no significant cognitive differences, researchers said.
Executive functioning includes the ability to shift attention between two different parts of a task. Verbal memory is the ability to retain and recall spoken information.
Researchers were at a loss to explain why tamoxifen caused a drop in cognitive abilities, but there have been a number of studies that link estrogen with verbal memory, including a 2004 study by U.S. researchers who found that estrogen boosted long-term memory in men, and other studies that suggest women tend to have better verbal memory skills than their male counterparts.
The results of the new study comes on the heels of other research involving the drug, published in the most recent issue of the British Medical Journal, which found that selective serotonin reuptake inhibitors (SSRIs), like Paxil, can interfere with tamoxifen, reducing or completely mitigating the breast cancer drug’s effects. SSRIs are often prescribed to breast cancer patients to combat depression.