Drugs for prevention of breast cancer

By Dr. Ananya Mandal, MDMar 28 2011

According to an international panel of cancer experts, women at high risk of developing breast cancer should be given preventative drugs. The experts write in the Lancet Oncology adding, drugs such as tamoxifen could reduce the chances of developing breast cancer. They suggest that this would be something similar to prescribing statins to patients at risk of heart disease. But tamoxifen has been linked with womb cancer, blood clots and stroke.

In the UK, 46,000 women are diagnosed with breast cancer each year. Two drugs, tamoxifen and raloxifene, have been approved in the US for the prevention of breast cancer. However, they are not available as a preventative measure in the UK.

Chairman of the panel, Professor Jack Cuzick, is an epidemiologist at Queen Mary, University of London, He said, “The two drugs should be approved in the UK. The evidence for them is overwhelming.” He explained that for every 1000 women given tamoxifen there would be 20 fewer breast cancers, but there would also be three more womb cancers and six more cases of deep vein thrombosis. To balance the risks, the panel agreed that women who had a greater than 4% chance of developing breast cancer in the next 10 years should be offered preventative therapy.

Next come the challenges of predicting risk. In heart disease, there are well-known risk factors such as blood pressure and cholesterol, which can inform treatment. The challenge for any preventative breast cancer treatment would be identifying similar “markers” of risk. The panel suggests breast density. They say patients with more than 75% "dense breast tissue" had at least four times the risk of developing breast cancer than patients with mainly non-dense tissue. Professor Cuzick explained, “Increased breast density is one of the leading risk factors for breast cancer and early trial results suggest that where tamoxifen is shown to decrease density, the risk of cancer decreases…If this is confirmed in long-term studies, breast density could become a powerful way to identify high-risk women who could benefit from preventive treatments.” He suggests the risk of getting breast cancer should be determined during cancer screening.

Women with rare but incredibly destructive genes that make the development of breast cancer almost inevitable are already entitled to regular checks and some are given drugs to cut their chances of contracting the disease.

Meg McArthur, senior policy officer at Breakthrough Breast Cancer also said, “It is vital that we find effective ways to prevent breast cancer, especially in women with a high risk. However, as preventative therapy may have negative side effects it would not be appropriate for everyone…We welcome studies investigating the best treatments to be used for breast cancer prevention. It's also crucial to identify those at high-risk who would benefit the most from this form of therapy.” According to Dr Lesley Walker, from Cancer Research UK, “Our scientists were behind some of the first trials showing the long term benefits of tamoxifen for preventing breast cancer in women with a greater than average risk of the disease…Being able to accurately predict breast cancer risk and who will respond to preventative drugs like these is a crucial step in ensuring women get the most suitable treatment.”