Breast cancer subtypes are different diseases

There is a biological distinction between breast cancers that depend on hormones and those that do not, according to research published in PLoS Genetics (Friday).

Scientists previously thought that hormone dependent breast cancers, which usually require treatment with surgery and anti-hormone drugs, originated from the same biological pathway as hormone independent breast cancers, which are treated with surgery and chemotherapy.

The new discovery provides the strongest evidence yet that the subtypes originate from separate pathways and could guide future research into prevention and treatments for the cancer types as different diseases.

Currently, there are fewer treatment options for women with hormone independent breast cancer following surgery.

Cancer Research UK's Dr Paul Pharoah, lead author based at the University of Cambridge, 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."

In the largest study of its kind, the international collaborative effort** funded by Cancer Research UK looked at the genetic makeup of over 23,000 breast cancer cases.

Dr Lesley Walker, Cancer Research UK's director of cancer information, said: "Scientists were previously unsure how different types of breast cancer developed. Although the findings won't have any immediate effects on the treatment of women with the disease, they are important in helping to define the next steps in our research on the causes of this major cancer."

Notes

* Heterogeneity of breast cancer associations with five susceptibility loci by clinical and pathological characteristics. Montserrat Garcia-Closas et al. 2008. PLoS Genetics.

** The researchers in this study used data provided by the Breast Cancer Association Consortium (BCAC)- a huge international collaborative group of researchers interested in inherited risk of breast cancer. Co-ordination of BCAC is funded by Cancer Research UK.

Hormone dependent breast cancers are also known as ER positive and hormone independent breast cancers as ER negative.