A more effective therapy has emerged for preventing hormone-sensitive breast cancers returning in younger women.
A global study, published overnight in the New England Journal of Medicine, has shown that exemestane, an oestrogen supressor, was 34% more effective at reducing the risk of breast cancer returning in pre-menopausal women than tamoxifen, a standard post-breast cancer treatment.
The new treatment is effective for young women who have had hormone-sensitive breast cancer, which applies in eight out of 10 cases of breast cancer in younger women.
The results show that 92.8% of women treated with exemestane and oestrogen suppression treatments were free from breast cancer after five years, compared to 88.8 % for those treated with the widely-used therapy tamoxifen.
The hormone therapy study, involving two large clinical trials of almost 5000 pre-menopausal women from 27 countries, including Australia, compared the two treatments in combination with ovarian function suppression.
Oestrogen, made by the ovaries, can stimulate the creation of breast cancer cells. Exemestane works by blocking enzymes responsible for producing oestrogen, while tamoxifen blocks the uptake of oestrogen in breast tissue.
Associate Professor Prue Francis, from Melbourne’s Peter MacCallum Cancer Centre, one of the lead authors on the study, said recurrence of breast cancer was the most feared aspect of breast cancer.
“The results in the trials overall are very good, with 92.8% of the women assigned to treatment with exemestane plus ovarian function suppression remaining free from breast cancer over five years,” she said.
“Just over half the women in the trials also received chemotherapy as decided with their doctor.”
Professor Francis said the trials were another important step along the way to completely preventing recurrences of breast cancer.
Associate Professor Clare Scott, an oncologist from the Walter and Eliza Hall Institute, said the finding was an important example of incremental benefit.
“It might only sound like a few percent, but that is the way breast cancer outcomes have improved over the last 20 years for women with early breast cancer,” she said.
Professor Geoff Lindeman, joint head of breast cancer at the Walter and Eliza Hall Institute, said this was a landmark study, as it suggested that an aromatase inhibitor [exemestane] was a better choice than tamoxifen for women who elect to have their ovaries switched off for this long period of time.
“Since breast cancer is so common, this translates into a very important finding,” he said.
Professor Francis said in some countries the use of ovarian function suppression for young women with hormone sensitive early breast cancer was common.
“In these countries, the results will be rapidly practice-changing for treatment regimes,” she said.
“In other countries, ovarian function suppression has been less widely utilised, as there has been uncertainty as to its exact value, over and above the standard treatment of tamoxifen.”
Professor Lindeman said women who are simply on tamoxifen should not be worried by this new study.
“Tamoxifen remains a highly effective therapy that has saved more than a million lives to date,” he said.