It's good news for women who put their baby plans on hold so they can focus on their careers.
Those who wait until they are at least 28-years-old to have their first child could reduce their risk of the most deadly form of breast cancer by up to 60 per cent.
However, researchers from the Fred Hutchinson Cancer Research Center in Seattle found that breast feeding also has a protective affect against the drug-resistant form of the condition.
Waiting until you are 28 to have children could reduce your risk of developing an aggressive form of breast cancer before you're 50
The study, in pre-menopausal women, is the first to look at the relationship between a woman's first period and pregnancy and triple-negative breast cancer.
They found women who had their first child at least 15 years after their first period (on average experienced at 13) had a 60 per cent lower risk of developing the condition.
About 48,000 women get breast cancer in Britain each year. Most (80 per cent) are over 50 but younger women, and in rare cases men, can also develop it.
Triple-negative breast cancer affects around 15 per cent of sufferers and it is difficult to treat. Unlike other breast cancers it doesn't depend on hormones such as oestrogen to grow, so won't respond to hormone-blocking drugs such as Tamoxifen.
Previous research has shown that early pregnancy lowers the risk of the most common type of breast cancer, known as ER positive. Scientists believe the hormones of pregnancy trigger certain changes in the structure of the breast to make tissue less susceptible to the ER type of cancer.
However, scientists of the current study, found that with triple negative breast cancer, the later the pregnancy the lower the risk. They have yet to understand the reason behind this association.
Breastfeeding has a protective effect against triple negative breast cancer as well as giving immune-boosting properties for the baby
The study also confirmed several previous studies that have suggested that breast-feeding can also have a beneficial effect.
'Breast-feeding is emerging as a potentially strong protective factor against one of the most aggressive forms of breast cancer,' study leader Dr Christopher Li.
The research involved more than 1,960 women between the ages of 20 and 44, 1,021 with a history of breast cancer and 941 without.
Reproductive histories among women without a history of breast cancer were compared to those of women with different forms of breast cancer.
Dr Li said further research would be needed to confirm the findings. The study has been published in the journal Breast Cancer Research and Treatment.
Read more: http://www.dailymail.co.uk/health/article-2247602/Postponing-pregnancy-slashes-risk-deadly-form-breast-cancer.html#ixzz2Ey0YExrL
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