These data mark a breakthrough in hormonal breast cancer therapy as they clearly demonstrate that anastrozole is significantly more effective than the current 'gold standard' treatment tamoxifen in terms of
- improving disease-free survival for postmenopausal women with early breast cancer
- reducing the risk of endometrial cancer
- reducing incidence of hot flushes and thromboembolic events
The ATAC results show that anastrozole, an aromatase inhibitor (AI), is more effective in reducing the risk of cancer recurring in the same breast, the opposite breast, or elsewhere in the body when compared to tamoxifen. This is the first time an AI has been proved to be superior to tamoxifen in early breast cancer.
Anastrozole was also associated with a number of important tolerability advantages over tamoxifen – a key consideration in early breast cancer where women who are otherwise 'healthy' routinely take hormonal treatment for up to 5 years after initial tumour-removing surgery. Perhaps the most important of these, as presented in Oslo today, is the benefit of anastrozole in reducing the risk of developing abnormalities of the lining of the womb (endometrium) when compared to tamoxifen. Data presented from a sub-study of 279 trial patients*) demonstrated that anastrozole halved the risk of endometrial abnormalities compared to tamoxifen.
Speaking today at the UICC Congress, Dr Sean Duffy, from the Division of Obstetrics and Gynaecology at St James University Hospital in Leeds, UK, and lead ATAC sub-protocol investigator said; "This is an extremely important finding. Even though the risk of developing endometrial cancer when taking tamoxifen is small, and the benefits of this therapy far outweigh the risk, it has been a well known concern for doctors and their patients for some time. However, the ATAC study now demonstrates that anastrozole reduces the risk of endometrial cancer as well as the incidence of vaginal bleeding, compared to tamoxifen. This suggests that women treated with anastrozole are less likely to suffer the anxiety of having to undergo invasive procedures in hospital to rule out endometrial cancer as the cause of the bleeding."
Other tolerability advantages in favour of anastrozole reported at the UICC meeting today, include a significant reduction in the incidence of hot flushes and thromboembolic events such as deep vein thrombosis when compared to tamoxifen. Although the overall incidence of fractures was lower in the tamoxifen group, the incidence of hip fractures, which are associated with the highest mortality, was lower in the group treated with anastrozole (11 vs. 13 cases, respectively). Tamoxifen is known to have protective effects on bone in postmenopausal women and this may account for the difference in fracture rates between treatments to some extent.
ATAC is the largest cancer treatment trial ever conducted, involving over 9,300 post-menopausal women world-wide.
*) anastrozole n=99, tamoxifen n=92 combination treatment n=88