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THURSDAY, Feb. 11 (HealthDay News) -- The breast cancer drug tamoxifen -- used for three decades to treat the disease -- appears to affect cognitive abilities, including some types of memory, a new study has found.
"Our results are important for breast cancer patients because intact cognitive functioning is known to be an important precondition for well-being," said study author Christien Schilder, a doctoral student at the Netherlands Cancer Institute in Amsterdam.
After a year of taking tamoxifen (Nolvadex), women in the study scored lower on tests of verbal memory functioning and other cognitive skills than did women taking another breast cancer drug, exemestane (Aromasin).
Both drugs are considered hormone (or endocrine) therapy. Tamoxifen interferes with the activity of estrogen, which can promote the growth of breast cancer. Exemestane is an aromatase inhibitor, which decreases estrogen production in postmenopausal women.
Endocrine therapy is offered to many women with breast cancer, and "the choice for a specific endocrine agent and therapy sequence is, among others, based on the safety profile," Schilder said. "Therefore, we think that our results justify continuing research into the cognitive effects of endocrine therapy for breast cancer patients."
Schilder's study, funded by Pfizer, which makes Aromasin, was published online Feb. 8 in the Journal of Clinical Oncology.
For the study, the researchers gave neuropsychological evaluations to 299 women, including 179 with breast cancer. Testing was done at the start of the study and again after the women with breast cancer had had a year of hormone therapy -- 80 women taking tamoxifen and 99 taking exemestane.
The researchers found that tamoxifen users had lower scores in verbal memory and executive functioning -- which includes such things as being able to shift attention between two different parts of a task -- than did women without breast cancer. Women taking exemestane had smaller declines in these two areas, considered not statistically significant, compared with the healthy women, Schilder noted.
Those on tamoxifen also fared worse on information-processing speed than the exemestane users, the researchers found.
No substantial differences were found between any of the three groups in terms of visual memory, working memory, verbal fluency, reaction speed and motor speed, according to the study.
Exactly why the tamoxifen users fared worse is not known, Schilder said. "The mechanisms of action of tamoxifen on the brain are hardly known yet," she said, adding that one possibility is that tamoxifen might counteract possible beneficial action of estrogen on the brain.
Dr. Victor G. Vogel, vice president of research for the American Cancer Society, said the results were not surprising. And though the reason women on tamoxifen had more cognitive decline isn't known, he said a logical though unproven explanation is that "it may just not be good for your brain not to have estrogen."
However, Vogel emphasized that it's important to keep the study results in perspective, noting the life-saving benefits of tamoxifen.
According to the U.S. National Cancer Institute, "the benefits of tamoxifen as a treatment for breast cancer are firmly established and far outweigh the potential risks."
Said Vogel: "I'll take a little memory loss to keep my patients alive."
The American Cancer Society has more on tamoxifen.