Cancer Research Lab

Cardiovascular adverse events are relatively rare in early breast cancer patients during adjuvant endocrine therapy using letrozole or tamoxifen, but the type of such events differs depending on the agent employed, according to findings from the Breast International Group 1-98 study.

“The overall incidence of cardiotoxicity was small and similar with the two agents,” lead investigator Dr. Henning Mouridsen told Reuters Health, “although there was a one percent increased risk of more severe cardiotoxicity with letrozole. Tamoxifen was associated with a two percent increased risk of thromboembolic disease.”

In the December 20th issue of the Journal of Clinical Oncology, Dr. Mouridsen of Righospitalet, Copenhagen and colleagues report data on more than 7900 women with receptor-positive early breast cancer. They had been randomly assigned to 5 years of treatment with letrozole or tamoxifen or a sequence of these agents.

Adverse events were recorded until 30 days after completion of therapy or after switching agents in the sequential treatment groups. “Generally,” said Dr. Mouridsen, “letrozole and tamoxifen are both well tolerated.”

At a median follow-up of 30.1 months, the overall incidence of cardiovascular adverse events was 4.8% with letrozole and 4.7% with tamoxifen.

However, there were more grade 3 to 5 cardiac events with letrozole (2.4%) than with tamoxifen (1.4%). On the other hands, there were more thromboembolic events with tamoxifen (3.9%) than with letrozole (1.7%). This was also true of grade 3 to 5 thromboembolic events (2.3% versus 0.9%).

There were no significant between-group differences in the incidence of hypertension or cerebrovascular events.

Given the higher incidence of thromboembolic events with tamoxifen, the researchers suggest that patients at risk might consider avoiding such therapy.

They also point out that any excess of cardiac events on letrozole “seems to be outweighed by the superior control of locoregional and distant recurrence.”