Thousands of lives could be saved if more mothers breastfed, according to an American study.
Research on more than 750,000 women found breastfeeding was extremely effective at cutting the risk of developing the most aggressive forms of breast cancer.
The major study - which spanned four continents, and will be presented at San Antonio Breast Cancer Symposium in Texas - shows breastfeeding can cut the risk of developing breast cancer by one fifth.
Experts analysed 27 studies and found breastfeeding also reduced the most invasive breast cancers by around 10%.
The research, led by American cancer charities, with the Washington University School of Medicine and Mount Sinai Hospital, New York, found it not only protected against common types of breast cancer but against triple negative cancer, one of the most difficult to treat.
Thousands of cases of cancer could be prevented and lives saved if Britain improved rates of breastfeeding, which are the lowest in the western world, researchers said.
Just half of mothers in the UK are nursing their child at six weeks, and just one per cent follow NHS advice to provide their child with breast milk only until six months, official figures show.
Previous studies have suggested that breastfeeding has a protective effect against cancer, but have suggested the impact is relatively small.
Health expert Dr Hilary Jones spoke to Good Morning Britain about the findings of this study.