MedWire News: Breast cancers that require hormones to grow and those that do not need hormones to develop have different biological origins and are different diseases, say researchers.

Scientists previously believed that hormone-dependent breast tumours, which are usually treated with surgery and anti-hormone drugs, had the same biological origins as hormone-independent breast cancers, which are treated with surgery and chemotherapy.

The current findings contradict these assumptions and may eventually lead to improved treatments for women with breast cancer, says the team.

Dr Montserrat Garcia-Closas, from the National Cancer Institute in Rockville, Maryland, USA, and colleagues analysed the findings of 21 genetic studies involving more than 23,000 women with breast cancer.

The researchers examined the occurrence of five genetic variants that are known to be associated with breast cancer to see if they were more likely to be found in hormone-dependent or -independent breast tumours.

They found that one common variant of a gene called FGFR2 was strongly associated with hormone-dependent breast cancer, but weakly associated with hormone-independent cancer.

"This shows that [hormone-dependent and hormone-independent breast tumours] have distinct genetic origins and are different diseases," said study researcher Dr Paul Pharoah, from the University of Cambridge in the UK.

Commenting on the implications of their findings in the journal PloS Genetics, the researchers write: "The magnitude of the observed differences is small, and by themselves these findings are unlikely to have any immediate clinical implications.

"However, the observed differences provide clues to the biological mechanisms that underpin tumour [characteristics], which may ultimately lead to improved treatment and prevention."