Research has suggested that there is a biological distinction between breast cancers that depend on hormones and those that do not.
Scientists previously thought hormone dependent breast cancers, which usually require treatment with surgery and antihormone drugs, originated from the same biological pathway as hormone independent breast cancers, which are treated with surgery and chemotherapy.
But the new discovery, which is published in PLoS Genetics, provides the strongest evidence yet that the subtypes originate from separate pathways and therefore could guide future research into prevention and treatments for the cancer types as different diseases.
Cancer Research UK's Dr Paul Pharoah, who led the study, said: "We looked at five genetic variants associated with breast cancer to see if they were more likely to be found in hormone dependent or independent breast cancers.
"One common genetic variant, FGFR2, was strongly associated with hormone dependent breast cancer, but weakly associated with hormone independent cancer.
"This shows that they have distinct genetic origins, and are different diseases.
"We hope our study will help clarify the biology of breast cancer subtypes and steer future research along two, more distinct paths."