An international clinical trial has established that in postmenopausal women with early breast cancer, the drug letrozole offers better post-surgery protection against breast cancer recurrence than does tamoxifen, the current standard of care.
The clinical trial BIG 1-98 is being conducted under the auspices of the Breast International Group (BIG) and coordinated and managed by the International Breast Cancer Study Group (IBCSG). The IBCSG is an active member of the BIG organisation. In Australia and New Zealand the trial is being conducted by the Australian New Zealand Breast Cancer Trials Group (ANZ BCTG), based at the University of Newcastle.
It is the first clinical trial designed to test both a head-to-head comparison of letrozole or tamoxifen alone from the beginning of treatment and the sequencing of both agents during the first five years following breast cancer surgery.
The study involves postmenopausal women with early, hormone-sensitive breast cancer and is testing the following five year treatment plans:
• five years of tamoxifen alone versus five years of letrozole alone;
• the sequence of tamoxifen for two years followed by letrozole for three years;
• the sequence of letrozole for two years followed by tamoxifen for three years.
In 2005, first results from BIG 1-98 showed that letrozole for five years was superior to tamoxifen for five years in preventing breast cancer recurrence, especially distant recurrence. With this 2008 update there is a significant reduction in recurrences (including second malignancies and deaths prior to a cancer event).
The new data also suggests that, together with optimal surgery followed by chemotherapy and radiotherapy if needed, commencement of letrozole early in the treatment plan was the best way to remain free of cancer. This is especially true for patients with a higher likelihood of early recurrence, such as women who were found to have lymph nodes involved at the time of initial surgery.
Professor Alan Coates, Co-Chairman of the IBCSG Scientific Committee and lead investigator for the trial said, “The results of BIG 1-98 are of great importance to the majority of women with breast cancer. We already knew from our earlier results that letrozole alone is more effective than tamoxifen alone, but we did not know if giving both of the agents in a sequence (of letrozole followed by tamoxifen or tamoxifen followed by letrozole) would show superior results.”
“We found that it appears to be better to start treatment with letrozole and continue for five years, but if
necessary patients can switch to tamoxifen after two years without loss of efficacy.”
Professor John Forbes, University of Newcastle, Study Chair of BIG 1-98 for the ANZ BCTG and a Member of the BIG 1-98 International Steering Committee said, “This is an important trial. It is the only trial worldwide testing the value of continuous treatment with an aromatase inhibitor versus the sequencing of tamoxifen and letrozole. This new data reinforces our earlier results and confirms the importance of careful long-term follow-up after treatment has been completed to obtain this new data.”
How letrozole works
Many breast cancers are stimulated to grow by the natural hormone oestrogen. Tamoxifen, the current standard treatment, works by blocking the effect of oestrogen on breast cancer cells. A new class of anti-cancer drugs called aromatase inhibitors work by reducing the production of oestrogen in postmenopausal women thus depriving cancer cells of the source of oestrogen. Letrozole is an aromatase inhibitor.
For more information visit the Australian New Zealand Breast Cancer Trials Group website www.anzbctg.org