Women with a large bust may be more likely to develop breast cancer, according to scientists.
A study of 16,000 women found genetic mutations associated with breast size were also linked to the disease.
Researchers say some of these are involved in regulating the female sex hormone oestrogen, which can trigger the growth of both breasts and tumours.
While research has linked breast density the amount of non-fat tissue to an increased risk of cancer, there has been little evidence of a link with breast size before.
Participants in the study, carried out by a US company, were asked to give their bra size on a 10-point scale from smaller than AAA to larger than DDD.
The genetic code of the women – all of European origin was read by scientists who looked through millions of tiny mutations in their DNA, called single-nucleotide polymorphisms. Out of seven that were strongly linked to breast size, three were also associated with breast cancer.
Dr Nicholas Eriksson of the California-based genetics said it was the first substantial link between breast size and cancer, but added much more research was needed before it could be considered concrete.
He said: ‘Our results identify genetic variants that have an effect on both breast cancer and natural variation in breast size.
‘While the precise relationships between breast size, density, obesity and breast cancer remain difficult to untangle, understanding the biology . . . may aid in the development of novel screening tools.’
He said one of the three mutations regulates the activity of the oestrogen receptor gene that plays a vital role in breast growth and in the majority of breast cancer cases.