Study shows breast cancer 'is deadlier in young mums'

Dr Borges discovered that child-bearing triggers breast changes that cause cancerous cells to "behave much more aggressively". Photo / Getty Images

Breast cancer in young women is more likely to be fatal if it occurs after they've had a baby, according to a new study.

Changes to a woman's breasts triggered by bearing a child make it easier for cancer cells to spread, researchers found.

Oncologist Dr Virginia Borges, who led the University of Colorado study, said: "If a woman gets breast cancer before 45, it is far more aggressive and more likely to kill if she has had kids."

The study followed 701 US women diagnosed between 1980 and 2014 and before their 45th birthday.

Among women diagnosed in the early stages of cancer, those who had given birth less than 10 years before diagnosis were up to five times more likely to see the cancer spread, compared to non-mothers.

Borges discovered that child-bearing triggers breast changes that cause cancerous cells to "behave much more aggressively, increasing their ability to invade surrounding breast tissue and spread".

She stressed her findings did not mean becoming a mother increased the chances of breast cancer.

But she said motherhood was "a readily identifiable risk factor"for breast cancer aggressiveness which women and doctors needed to be aware of.