'Landmark' study could change future of breast cancer

Breast cancer can be reclassified into ten separate 'diseases' based on its genetic characteristics, according to scientists. Analysis of the DNA and RNA from almost 2,000 tumours identified ten genetically different subtypes of breast cancer with different survival outcomes. The information could be used to better predict the outcomes of the disease, as well as offer tailored treatment to patients.

'Our results will 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', said Professor Carlos Caldas, senior group leader at Cancer Research UK's Cambridge Research Institute.

To date, breast cancer has been classified either by looking at the cells it originates from, or what treatments it might respond to (by testing for oestrogen and progesterone receptors, for example).

'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', Professor Caldas added.

The team used tissue samples from women diagnosed with breast cancer between five and ten years ago. The samples came from tumour banks in the UK and Canada, and their age meant researchers knew what happened to the women after their tumours had been removed.

They mapped three types of genetic mutations in the tumours: copy number variants, which happen when a cell divides and accidentally copies a piece of DNA more than once; SNPs, in which one single letter of DNA has changed; and gene-expression data, which measures RNA to gauge the activity of particular genes.

This allowed the team to divide a subset of 997 tumours into ten groups of genetically similar breast cancers. They then repeated this on a separate group of 995 tumours to confirm their initial results.

'The size of this study is unprecedented and provides insights into the disease such as the role of immune response, which will stimulate other avenues of research', said Professor Samuel Aparicio, co-lead author of the study, based at the BC Cancer Agency in Vancouver.

The study has resulted in a comprehensive map of breast cancer genes, some of which were already known (such as BRCA2, an important gene in heritable breast cancer). But it has also discovered several completely new genes that had not been associated with breast cancer before. These genes provide potential targets for novel breast cancer treatments.