Younger women's breast cancer is genetically different
US scientists have discovered sets of genes that are often switched on in breast tumour cells from young women but not in those from older women.
The discovery may help to explain why breast cancer in young women is often more aggressive and does not respond as well to treatment as breast cancer in women over the age of 45.
But despite being generally more aggressive, the disease is relatively rare in younger women, with two thirds of cases occurring in women over 65.
Researchers at Duke Comprehensive Cancer Centre and the Duke Institute for Genome Sciences & Policy studied tumour samples from nearly 800 women with breast cancer in five different countries.
When the tumours were divided into groups depending on the women's ages, the researchers identified more than 350 sets of genes that were only switched on in tumours from the younger women.
Genes involved in regulating immune function, oxygen supply and DNA repair - such as BRCA1 - tended to be switched on in younger women's tumours, but not in those taken from older women.
Senior investigator Dr Kimberly Blackwell, who is a breast cancer specialist at Duke, said that the discovery was "truly remarkable".
"Clinicians have long noted that the breast cancers we see in women under the age of 45 tend to respond less well to treatment and have higher recurrence rates than the disease we see in older women, particularly those over the age of 65," she noted.
"Now we're really understanding why this is the case, and by understanding this, we may be able to develop better and more targeted therapies to treat these younger women."
Dr Blackwell noted that finding out which sets of genes are switched on in the tumour cells of younger breast cancer patients could help researchers to develop new therapies.
"Many of the gene sets we saw in 'younger' tumours distinguished these cancers from 'older' tumours but the reverse was not true - there was nothing we saw in the older women's tumours that set them apart genomically," she explained.
"Identifying these distinguishing characteristics may be the first step in developing more effective treatments for these younger patients."
The findings are published in the Journal of Clinical Oncology.