Researchers test whether drug can prevent breast cancer in healthy women
Wednesday, March 30, 2005
TORONTO (CP) – Researchers in Canada and the United States are embarking on a clinical trial to see if a drug which is highly effective in treating breast cancer could be used to prevent it. The five-year study, led by renowned breast cancer researcher Dr. Paul Goss, should answer the question of whether drugs called aromatase inhibitors have a role to play in disease prevention in women after they go through menopause – the time of life when three-quarters of breast cancers are diagnosed. Goss, who is conducting a number of ongoing treatment studies with this class of drugs, said the prevention trial – launched Wednesday – was 10 years in the planning. “For us it’s the real cherry on the cake and we’re very, very excited about it,” he said from Boston, where he is director of breast cancer research at Massachusetts General Hospital Cancer Center. “We’re fairly sure it’s going to work well too.” The trial is being co-ordinated by the National Cancer Institute of Canada clinical trials group and is funded in part by the Canadian Cancer Society. Currently there is little that doctors can offer women who are at high risk of developing breast cancer, apart from the always sage advice to eat a healthy diet and exercise. The one drug currently proven to help prevent breast cancer, tamoxifen, has significant side-effects, such as the risk of developing deep vein thrombosis (blood clots) and uterine cancer. Running those risks may make sense to a woman who has had cancer and fears a recurrence. But women who don’t know whether they will develop the disease have been reluctant to take them on. “If successful, this clinical trial really has the opportunity to offer another option for women who are at increased risk of developing breast cancer,” said Sarah Bouma, senior manager for research with the Canadian Cancer Society, Ontario division. One of the Canadian investigators said a positive outcome could lead to a day when menopausal women will routinely sit down with their doctors to figure out whether breast cancer prevention therapy makes sense for them. “If this trial does establish that this drug not only reduces the incidence of breast cancer – which I am pretty optimistic it will – but also is safe and tolerable by the majority of women, I think that that type of conversation may become something that is common in doctors’ offices,” said Dr. Eric Winquist, a medical oncologist at the London Health Sciences Centre in London, Ont. But Goss does not anticipate a future in which all menopausal women would be offered this drug, exemestane, for cancer prevention. In fact, he’s hoping this trial, named the ExCel study, will help determine who would benefit and who would not. “We believe at the conclusion of this trial we will be able to say: ‘You know what? Not everyone who entered this trial did need it in hindsight.’ But we strongly believe we can’t find that out without doing the trial,” explained Goss, who until last year practised at Princess Margaret Hospital in Toronto. It’s hoped that 4,500 healthy post-menopausal women who are considered at high risk will be enrolled in Canada, the United States and Spain. High risk is determined by using a tool called a Gail score, which looks at a woman’s age, family breast cancer history, age of first menstrual period, age at the time of first live birth and number of previous breast biopsies. Half will receive exemestane and the other half will receive a placebo. Neither the women nor their doctors will know who is getting which. Treatment will continue for five years and the women will be followed well after that, Goss said, to compare breast cancer rates among those who took the drug and those who did not. But it is expected that initial results of the study may be available within about four years. Janet Adams, a nurse from Port Hope, Ont., is one of two Canadians who’ve already enrolled. Adams has been taking her daily pill since December. She feels no real side-effects – exemestane can cause mild nausea and hot flashes – and suspects she is in the placebo arm. Still, she believes it’s important to help find whether this drug can cut the rate of breast cancer. Breast cancer is the most commonly diagnosed cancer in Canadian women and is the second leading cause of cancer deaths in women in this country. “It’s more for my daughter,” Adams said. “For my daughter’s generation. I may be on the placebo and not getting any of the benefits of the exemestane. In five years the results will be out and we will know whether it does prevent breast cancer or not. So when my daughter’s of the age, she’ll be able to take the pill, hopefully, to prevent breast cancer.” There is evidence to suggest the drug may work. For instance, it’s been shown to prevent the occurrence of new cancers in the opposite breast in women who have already had a breast cancer. The drug works by suppressing estrogen, which fuels the growth of most breast cancers. Unlike other aromatase inhibitors, it is not believed that women who take it run a higher risk of developing osteoporosis. The drug is made by Pfizer. The company is donating the needed drugs for the trial.
© The Canadian Press 2005