Breast cancer treatment for young women should be managed in a way which is distinct from current methods.
Researchers told the fourth IMPAKT Breast Cancer Conference in Brussels that this is because the disease is biologically unique from forms of the disease seen in older patients.
Patients under the age of 40 are often diagnosed when the disease is at an advanced stage and as a result their prognosis is poor.
There are several genes and genetic signatures that are significantly associated with age in breast cancer patients, said Dr Hatem Azim, lead author of the study.
"Some were highly expressed in young women - including stem cells, luminal progenitors, RANK-ligand and c-kit - while others were down-regulated, such as genes related to programmed cell death, or apoptosis," he added.
These factors make it much more likely that the tumours will spread to other areas of the body, which may account for the lower survival rate, the doctors explained.