Survival benefit for Arimidex in early breast cancer compared with Tamoxifen

Data presented at the San Antonio Breast Cancer Symposium ( SABCS ), Texas has found that Arimidex ( Anastrozole ) is the first aromatase inhibitor to provide an overall survival benefit, compared with Tamoxifen, in the treatment of hormone-sensitive early breast cancer.

According to this new analysis of data, by replacing Tamoxifen with Arimidex, postmenopausal women being treated for early breast cancer may almost halve the likelihood of their disease returning and reduce their risk of dying by nearly a third.

“ For the first time, an aromatase inhibitor has shown a survival advantage over Tamoxifen in early breast cancer. These studies, along with others such as the ATAC trial, confirm that Tamoxifen is no longer the best option we can offer our patients. Women who have taken two years of Tamoxifen should be switched to Anastrozole at the earliest opportunity to give them the best chance of surviving their disease,” commented Walter Jonat of University of Kiel, Germany, the key investigator who presented the new data at the SABCS.

Three key international trials ( ABCSG - Austrian Breast & Colorectal Cancer Study Group 8 , ARNO - Arimidex-Nolvadex 95, and ITA – Italian Tamoxifen Anastrozole ) were similarly designed to assess, in women already being treated with Tamoxifen, whether or not replacing Tamoxifen therapy with Anastrozole after 2-3 years was more effective than remaining on Tamoxifen for the full five year treatment period.

The meta-analysis of these three trials showed at a median follow-up of 30 months, patients who started taking Anastrozole, rather than remaining on Tamoxifen, experienced a:

- 29 per cent improvement in overall survival ( HR 0.71; p=0.0377 );

- 45 per cent improvement in event-free survival ( HR 0.55; p<0.0001 );

- 39 per cent improvement in distant recurrence-free survival ( HR 0.61; p=0.0015 )

These data now confirm that replacing Tamoxifen with Anastrozole can significantly reduce recurrence, prevent metastatic spread and ultimately save the lives of many women with early breast cancer.

Recent evidence and opinion have shown that women newly diagnosed with hormone-sensitive early breast cancer should be started on Anastrozole as the initial hormonal treatment after surgery.
In ATAC ( Arimidex, Tamoxifen, Alone or in Combination ) Trial, women taking Anastrozole for the full five year treatment period had a significantly reduced risk of disease recurrence ( including distant disease recurrence and contralateral breast cancer ), compared with Tamoxifen, especially during the first three years following surgery, when this risk is greatest.
Additionally, these women suffered far fewer serious side effects, including an increased risk of endometrial cancer, thromboembolic events and ischaemic cerebrovascular events, than those who were started on Tamoxifen.
Although Anastrozole, like all aromatase inhibitors increases the risk of bone fracture compared with Tamoxifen, it is possible to predict which women may be most at risk of fracture and manage them accordingly. This is not the case with the more serious side effects associated with Tamoxifen.

“ The ATAC trial has confirmed that starting treatment with Anastrozole at the earliest opportunity after surgery, and giving it for the full five years of treatment, is more effective than Tamoxifen for the prevention of disease recurrence. This would suggest that the best place to use Anastrozole is right from the start. These new data are important news for women currently taking Tamoxifen who can still gain from the significant benefits of anastrozole by switching at two years.” commented Jeffrey Tobias of the University College London Hospitals, London ( UK ).

Source: AstraZeneca, 2005