Exemestane to replace Nolvadex For Breast Cancer Therapy
Read an interesting article in the Toronto Star this morning:
Cut/Paste:
A decades-old, tried-and-true breast cancer drug could be knocked out of the treatment regimen after a groundbreaking study found newer drugs work better at preventing recurrence of the disease.
Switching from the anti-cancer drug tamoxifen to exemestane after two years of treatment cut a woman's risk of suffering another bout of cancer by one-third compared with women who took tamoxifen for the recommended five years, according to a major study published today in the New England Journal of Medicine.
The finding flies in the face of the accepted gold-standard treatment, in which breast cancer survivors are treated first with surgery and radiation, followed up with tamoxifen for five years if the cancer spreads.
"My belief is that this result should change clinical practice. I cannot envisage a patient wishing to complete five years of tamoxifen when this particular added advantage could be obtained by making the switch," said Dr. Paul Goss, director of breast cancer prevention at Princess Margaret Hospital.
The British study, sponsored by the drug's maker, Pfizer, followed 4,700 post-menopausal women in 37 countries.
It found that exemestane not only helped more women remain free of disease, but also produced far fewer side-effects than tamoxifen.
Women who were switched over to exemestane, sold under the brand name Aromasin, were 56 per cent less likely to get cancer in the other breast and half as likely elsewhere in the body, according to the study.
"I know of no other class of drug that has such an impact on the outcome of people with such a common cancer," Goss said. "To give you a sense of it, it outstrips any chemotherapy advances that we've seen for breast cancer patients in the past."
Researchers considered the study's findings so promising they reported their results early to give more women the option of starting on the therapy.
About 1.5 million worldwide are currently taking tamoxifen to prevent a breast cancer relapse. About one in nine women will develop breast cancer in the course of her lifetime; one in 27 will die of it.
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`We are sitting in the middle of a revolution in ... the outcome of breast cancer'
Dr. Paul Goss, Princess Margaret Hospital
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"It's a good thing that people need to know about and it's a good thing that different treatments are being offered," said Sue Wright, a breast cancer survivor who now works at Willow Breast Cancer Support and Resource Services, a clearinghouse of information on the latest treatments for breast cancer.
Exemestane belongs to a class of drugs known as aromatase inhibitors, which work by cutting off the supply of estrogen that breast cancer cells need to survive and reproduce. Although there are three types of aromatase inhibitors, none is currently licensed for use in Canada as supportive therapy in breast cancer survivors.
"I think we're in a process of changing that," said Dr. Kathy Pritchard, the head of breast cancer research at Sunnybrook & Women's College Health Sciences Centre. A massive Canadian study is being set up to test which of the aromatase inhibitors works best.
Pritchard notes that although Health Canada has approved exemestane only for use in women with advanced breast cancer, some doctors will still prescribe it as a preventative therapy.
"Are we a little behind in that approval? Yes, I think we are," Goss said simply.
Tamoxifen works by simply blocking cancer cells' access to estrogen, but it can have its own hormonal effect that is sometimes beneficial to cancer cells. Studies have also shown that cancer cells develop resistance to it in as little as a year.
"Tamoxifen has held centre stage for 30 years at least," Goss said. "It is probably the single most important anti-cancer drug ever discovered for any solid-tumour cancer, and we are now seeing it being ushered politely off stage."
Goss made headlines last fall when his own study found that following five years of tamoxifen therapy with a course of aromatase inhibitors could cut a woman's chance of recurrent breast cancer by half.
The only worry is that while tamoxifen's side effects are well known, newer drugs may prove to have long-term effects that will limit their use in some women, Pritchard said.
"We know this is not going to cure all breast cancer patients, and there is going to be some resistance," Goss said. Though the study looked only at post-menopausal women, he figures younger women could benefit, too, if the ovary was also blocked from producing estrogen. "Biologically, there's nothing to suggest that this strategy wouldn't be equally effective," he said.
"We are sitting in the middle of a revolution in terms of the outcome of breast cancer."
