A new prospective study has reported that adjuvant tamoxifen impairs some aspects of cognitive functioning among postmenopausal women with breast cancer whereas Aromasin (exemestane), an aromatase inhibitor, does not. The study included a total of 299 Dutch women in a randomized study evaluating tamoxifen versus Aromasin as adjuvant therapy for hormone sensitive breast cancer. Participants included 80 tamoxifen users, 99 Aromasin users, and 120 cancer-free controls. None of the women received chemotherapy as part of their breast cancer treatment. The women underwent neuropsychological assessment before beginning either tamoxifen or Aromasin and one year after treatment.

Tamoxifen users were found to perform worse than healthy controls on verbal memory and executive functioning (ability to organize thoughts and activities, manage time well, prioritize tasks, and make decisions) after one year, after adjusting for baseline performance. On the other hand, Aromasin users were found not to perform worse than healthy controls on any cognitive measures. Tamoxifen users also performed worse than Aromasin users on information processing speed after one year. However, no significant differences were observed between tamoxifen users, Aromasin users, and healthy controls with respect to verbal fluency, visual memory, working memory, reaction speed, and motor speed. The authors conclude that tamoxifen use is associated with significantly lower functioning in verbal memory and executive functioning, whereas Aromasin use is not associated with impaired cognitive functioning in postmenopausal women with breast cancer. The results highlight the need to include assessments of cognitive effects of adjuvant endocrine treatment in long-term safety studies.

Tamoxifen versus Aromasin

While previous studies have also found that tamoxifen use can impair cognition, this is not a well known side effect of the drug. Aromatase inhibitors such as Aromasin, Arimidex (anastrozole) and Femara (letrozole) have been found to be more effect than tamoxifen in treating hormone receptor positive breast cancer in many cases. For example, one study found that switching postmenopausal women with early breast cancer to Aromasin after two or three years of tamoxifen rather than having them stay on tamoxifen for five years reduces the risks of recurrence and death. While aromatase inhibitors share some of the side effects of tamoxifen (resulting from estrogen deprivation), cognitive impairment does not appear to be among them, at least in the case of Aromasin.