Newer breast cancer drug seen safer than tamoxifen

By Anthony J. Brown, MD

NEW YORK (Reuters Health) – As add-on therapy for
early-stage breast cancer, the drug anastrozole, known by the
brand name Arimidex, is less likely than tamoxifen to cause
adverse effects, including serious events and those leading to
treatment discontinuation, new research suggests.

In 2005, the results of the “Arimidex, Tamoxifen, Alone or
in Combination (ATAC) trial were published and showed a benefit
for Arimidex over tamoxifen in terms of disease-free survival,”
Dr. Joan Houghton, from University College London, told Reuters
Health. “With the current analysis, we just wanted to make sure
Arimidex was as safe as tamoxifen.”

Arimidex does increase the risk of bone fractures, which
Houghton said was anticipated, but the risk does not extend
beyond the treatment phase and is easily managed. However, the
newer agent has a better safety profile than tamoxifen.

The current ATAC analysis, which appears in the medical
journal Lancet Oncology, includes follow-up data for 3125 women
who completed 5 years of treatment with anastrozole and 3116
similar women treated with tamoxifen. The average follow-up
period was 68 months.

The overall rate of side effects was significantly lower
with anastrozole than with tamoxifen: 61 percent vs. 68
percent. Serious side effects were nearly half as common with
anastrozole: 5 percent vs. 9 percent.

Eleven percent of anastrozole-treated patients experienced
side effects leading to treatment discontinuation compared with
14 percent of tamoxifen-treated patients.

Tamoxifen has received much praise since it first became
available in the 1970s, but, Houghton said, the newer types of
drugs such as anastrozole “have really knocked tamoxifen off
its perch.”

The study was funded by AstraZeneca, which developed both
Arimidex and tamoxifen (Nolvadex), although the latter agent
has been available in a generic form for several years.

SOURCE: Lancet Oncology, August 2006.