Later childbearing 'lowers risk of aggressive breast cancer' Those who wait at least 15 years after the onset of puberty before having their first child, are at a 60 per cent lower risk of being diagnosed with triple-negative breast cancer, according to the study by the Fred Hutchinson Cancer Research Centre in Seattle, US. Triple-negative breast cancer accounts for about one in seven cases in Britain, meaning roughly 6,000 woman a year are told they have it. The disease, which tends to develop at a younger age than other types of breast cancer, is resistant to many forms of treatment such as the drug tamoxifen. As a result women tend to die of it sooner. Dr Christopher Li, from the centre's Public Health Sciences Division, said: "We found that the interval between menarche [first period] and age at first live birth is inversely associated with the risk of triple-negative breast cancer." The study results, published online in the journal Breast Cancer Research and Treatment, also showed that women who breast fed were less likely to develop triple-negative breast cancer. It 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 three types of breast cancer: ER-positive (781), triple-negative (180) and HER2-overexpressing (60). Delaying childbearing had no impact on the chances of getting the other two types of breast cancer. Dr Li noted: "This is an observational study and also one of the first to focus on premenopausal breast cancer and so our results require confirmation and thus should be interpreted with some caution."