New results show that postmenopausal women with breast cancer receiving adjuvant letrozole have better cognitive function than women being treated with tamoxifen. The data, from a recent meeting of the American Society of Clinical Oncology (ASCO), are drawn from a sub-study of the Breast International Group (BIG) 1-98 trial.

The trial, which enrolled postmenopausal women surgically treated for early-stage, hormone-responsive breast cancer, found that letrozole was more effective at preventing recurrent disease (especially distant metastases) than tamoxifen.

Karen E. Ribi, PhD, with the International Breast Cancer Study Group in Bern, Switzerland, and her colleagues had theorized that because of the estrogen deprivation associated with aromatase inhibitors, patients who have received letrozole will have worse cognitive function than tamoxifen-treated patients.

“While cognitive function is recognized as a potential long-term side effect of adjuvant chemotherapy for breast cancer treatment, few studies have looked at the effect of adjuvant endocrine therapy on cognition,” Dr. Ribi noted in her presentation. “What’s more, those studies that have examined the effect of adjuvant endocrine therapy on cognition have produced conflicting results.”

The primary endpoint of the sub-study was the composite score calculated from seven cognitive tasks. These included detection, identification, learning, memory, monitoring, shopping list, and shopping list delayed recall.

The analysis included 120 women enrolled in an institution with at least ten patients recruited to the parent protocol. All women had been in the trial for fewer than five years and were still taking their assigned endocrine treatment. None had developed recurrent breast cancer or a second malignancy.

Results showed that that while both groups had scores below age-standardized standardized norms of the CogState tasks, patients taking letrozole during the last three of five years of treatment had better cognitive function than those taking tamoxifen.

Dr. Ribi cautioned that potential study limitations include the lack of a true baseline assessment prior to the start of endocrine therapy and the lack of a longitudinal design to evaluate changes during treatment. Also, the sub-study’s low accrual resulted in a revised analysis plan.

Finally, she said that future trials will evaluate the change in cognitive function from five years on endocrine treatment to one year after the completion of treatment. Plans are also underway to examine the impact of endocrine treatment on cognitive function in premenopausal women from baseline to one year on treatment.

Written by Jill Stein
Jill Stein is a Paris-based freelance medical writer.