A landmark study has revealed there are 10 different types of breast cancer, not four as previously thought - a finding that is expected to have far-reaching implications for treatment of the disease.
The research by British and Canadian scientists, published today in the journal Nature, is the largest global gene study of breast cancer tissue ever performed, and the culmination of decades of research into the disease.
Carlos Caldas, one of the authors and the chairman of cancer medicine at the University of Cambridge, said the results would “pave the way for doctors in the future to diagnose the type of breast cancer a woman has, the types of drugs that will work, and those that won’t, in a much more precise way than is currently possible.”
Breast malignancies are diagnosed in almost 1.4 million women a year worldwide, and are especially prevalent in Europe, Australia, New Zealand and north America, according to the World Cancer Research Fund.
They are the most common type of cancer among Australian women, and the second most common cause of cancer-related death after lung cancer, figures show. The number of women diagnosed with breast cancer in Australia increased from 5291 in 1982 to 12,567 in 2007, and is forecast to rise again to 15,409 in 2015.
Sandra O’Toole, a Clinical Associate Professor from the University of Sydney Medical School, said the new findings were “very powerful” because they “present new information on genes that might give rise to new targeted treatments in the future. For example one subtype of breast cancer looks to be influenced strongly by the immune system which may lead to new approaches to treatment.”
Until now, doctors have classified tumours into one of four types by looking at the tissue under a microscope. The category of tumour has provided a guide to how long a woman is likely to survive and which drugs to use.
But doctors were at a loss to explain why, in some cases, treatments turned out to be ineffective, and in others, supposedly dangerous tumours proved easy to beat.
The researchers, from Cancer Research UK’s Cambridge Research Institute and the BC Cancer Agency in Vancouver, believe their findings have solved the mystery.
The team analysed the DNA and RNA of 2,000 tumour samples from women diagnosed with breast cancer between five and 10 years ago, and were able to classify breast cancer into at least 10 new subtypes grouped by common genetic features that correlate with survival. The new classification could change the way drugs were tailored to treat women with breast cancer, they said.
The team also discovered several new breast cancer genes that drive the disease, all of which were potential targets for new types of drugs.
Tests to diagnose the new subtypes could be ready and in regular use in three to five years, Professor Caldas said. “It’s surely going to change the way we do clinical trials. It will lead to better treatments and more targeted treatments.”
“We’ve drilled down into the fundamental detail of the biological causes of breast cancer in a comprehensive genetic study. Based on our results, we’ve reclassified breast cancer into 10 types – making breast cancer an umbrella term for an even greater number of diseases.
"Essentially we’ve moved from knowing what a breast tumour looks like under a microscope to pinpointing its molecular anatomy – and eventually we’ll know which drugs it will respond to.
"The next stage is to discover how tumours in each subgroup behave – for example, do they grow or spread quickly? And we need to carry out more research in the laboratory and in patients to confirm the most effective treatment plan for each of the 10 types of breast cancer.”
Professor O'Toole added the study was “very powerful as it uses a very large number of cancer samples and tests the results in two different, large groups of patients, giving greater confidence in the findings.”