Research team from the Queen Mary University of London reports on the effectiveness of anastrozole as a prophylactic therapy in postmenopausal women.
Breast cancer is the most common cancer in women and affects over 55,000 UK women each year, killing more than 11,000. It is estimated that more than 2 million women across the world developed the disease last year, with more than 600,000 deaths.
Anastrozole, which inhibits the production of oestrogen in postmenopausal women, has been used to treat breast cancer in that group for more than 20 years. The first phase of this study, which was published in 2013, established its value as a prophylactic therapy. It reported that breast cancer occurrence amongst women taking the drug fell by 53 percent. It was recommended for preventive use by the National Institute for Health and Care Excellence in the UK in 2017 and by the US Preventive Services Task Force earlier this year.
However, the drug is not currently offered to all the women who could benefit – possibly because some physicians are unsure of the evidence base for long term impact.
The study led by Professor Jack Cuzick of Queen Mary University of London confirmed significant long-term use of the drug for protection for women who take it for five years and stop. The results showed that there was a 49 percent lower breast cancer incidence amongst participants who last took the drug seven years since the end of the trial compared to women who were given a placebo.
Professor Cuzick, who is co-chairman of International Breast Cancer Intervention Studies (IBIS), also presented the findings of the IBIS-II trial at the San Antonio Breast Cancer Symposium in Texas on 12 December 2019.
He said: “Previous research has confirmed that anastrozole is very effective while women are still taking the drug, but this is the only trial looking at whether it offers long term protection for women at high risk of developing breast cancer. After a detailed analysis of the IBIS-II data, we have concluded that it is highly effective in reducing breast cancer occurrence for at least 12 years.”
Dr Ivana Sestak, Reader in Medical Statistics at Queen Mary, said: “The findings mean that for every 29 women taking anastrozole for five years, one case of breast cancer will be prevented during a 12-year period. Around 49 women would need to take tamoxifen for five years to prevent one breast cancer case during the same period.”
Professor Cuzick highlights that this study provides a strong case for anastrozole as the drug of choice for post-menopausal women at high risk of developing breast cancer. Having said that, Professor Cuzick also notes that with the few deaths from breast cancer among trial participants, longer follow-up studies will be needed to evaluate whether anastrozole can reduce deaths from breast cancer.
The latest report also confirms that anastrozole does not have the same type of long-term side-effects associated with tamoxifen – including endometrial cancer.
Cancer Research UK, the Breast Cancer Research Foundation, Sanofi Aventis, Astra Zeneca and the National Health and Medical Research Council Australia funded the research.
The study was published in December 2019 on The Lancet. [APBN]