A major international study released in Toronto on Thursday offers new hope to breast cancer patients, showing that the drug letrozole appears to reduce the risk of recurrence of the disease by almost half in postmenopausal women.
Initial results of the Canadian-led research, involving more than 5,100 women with the most common form of breast cancer, were so strong that the trial was halted halfway through its planned five-year time span.
A mid-study assessment of results found that women with estrogen-sensitive breast cancer who had completed five years of tamoxifen treatment and then took letrozole were about 40 per cent less likely to have the cancer return or get a new tumour in the other breast than those who received a dummy pill after tamoxifen.
Deaths from breast cancer were also reduced. Seventeen women taking the placebo died of breast cancer, compared with nine taking letrozole.
“The results of this study unquestionably offer new hope to hundreds of thousands of breast cancer patients and their families,” Dr. Paul Goss, lead investigator for the study, said at a press conference in Toronto on Thursday.
The study, conducted by 18 doctors from various Canadian, U.S. and European hospitals, universities and cancer centres, aimed to build on the effectiveness of the drug tamoxifen.
That drug is the top treatment to stall tumour growth by preventing estrogen — which fuels the growth of about half of all breast cancers — from linking up to a receptor on the surface of cancer cells. Previous studies have found that tamoxifen's effectiveness ends after five years of use.
“More than half of women who develop recurrent breast cancer do so more than five years after their original diagnosis,” Dr. Goss said. “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.”
Letrozole, made by Novartis Pharmaceuticals, is an aromatase inhibitor that works by blocking production of estrogen. Side effects include increased risk of osteoporosis, hot flashes, night sweats and pain in the bones, joints or back.
“The important thing is that this pill is really safe,” Dr. Gross said. “This drug appears to be extremely well tolerated.”
The study was also published on-line Thursday by the New England Journal of Medicine. The journal moved up publication of the study, which will appear in the Nov. 6 issue, because of the importance of the findings.
The researchers are notifying the 5,187 women worldwide who participated in the study. Women on letrozole will continue taking the drug and those on the placebo can begin taking letrozole, if they choose to.
“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,” said Dr. James Ingle, a Mayo Clinic medical oncologist and leader of the research study in the United States.
With Canadian Cancer Society funding, the clinical trial was co-ordinated 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.
Dr. Barbara Whylie, director of cancer control policy for the Canadian Cancer Society, said the results will be welcomed news for the thousands of Canadian women battling the disease.
“We estimate that more than 20,000 Canadian women will be diagnosed with breast cancer this year and just over half of those are going to be eligible for this drug,” she said. “That means these women will have a significantly improved hope for a future without cancer.”
