A Canadian-led international clinical trial has found that post-menopausal survivors of early-stage breast
cancer who took the drug letrozole after completing an initial five years of tamoxifen therapy had a
significantly reduced risk of cancer recurrence compared to women taking a placebo. The results of the
study appear in today?s advance on-line edition of the New England Journal of Medicine.

The clinical trial has been halted early because of the positive results and researchers are notifying the 5,187
women worldwide who have participated in the study. Women on letrozole will continue taking the drug
and those on the placebo can begin taking letrozole, if they wish.

?This very important advance in breast cancer treatment will improve the outlook for many thousands of
women,? said Andrew von Eschenbach, M.D., director of the National Cancer Institute which led the
study in the United States. ?This is one more example of the ability to interrupt the progression of a cancer
using a drug that blocks a crucial metabolic pathway in the tumor cell.?

Study researchers found that letrozole, when taken after five years of tamoxifen therapy, substantially
increased the chance of remaining cancer free. In total, 132 women taking the placebo had their disease
recur compared to 75 on letrozole. Overall, letrozole reduced the risk of recurrence by 43 percent, so that
after four years of participating in the trial, 13 percent of the women on the placebo, but only seven percent,
of those on letrozole had recurred. Deaths from breast cancer were also reduced. Seventeen women taking
the placebo died of breast cancer compared to nine taking letrozole.

While tamoxifen is widely used to prevent breast cancer recurrence in post-menopausal women, it stops
being effective after five years because, researchers believe, tumours become resistant to it.

?More than half of women who develop recurrent breast cancer do so more than five years after their
original diagnosis,? says Paul Goss, M.D., of Princess Margaret Hospital in Toronto. ?For years, we have
thought that we had reached the limit of what we could do to reduce the risk of recurrence with five years
of tamoxifen. Our study ushers in a new era of hope by cutting these ongoing recurrences and deaths from
breast cancer after tamoxifen by almost one half.? Goss, a leading expert in novel hormone therapies for
the treatment and prevention of breast cancer, conceived and chaired the international trial with letrozole.

A form of hormone therapy for the treatment of breast cancer, letrozole works by limiting the ability of an
enzyme called aromatase to produce estrogen, a major growth stimulant in many breast cancers.

Mayo Clinic medical oncologist James Ingle, M.D., says, "Based on our findings, all post-menopausal
women with hormone-receptor positive tumours completing about five years of tamoxifen should discuss
taking letrozole with their doctors to reduce their risk of breast cancer recurrence." Ingle, from Rochester,
Minn., led the research study in the United States.

With Canadian Cancer Society funding, the clinical trial was coordinated by the National Cancer Institute of
Canada Clinical Trials Group at Queen?s University, in partnership with the U.S. National Cancer Institute
and its Clinical Trials Cooperative Groups. Novartis, which manufactures letrozole, also known as
Femara?, provided the drug for the trial.

Women participated in the study for an average of 2.4 years and for as long as five years. The study found
that women taking letrozole had a reduction in the number of recurrences of cancer in their previously
affected breast, a reduction in the number of new cancers in their opposite breast, and a reduction in the
spread of the cancer outside their breast.