Researchers at the University of Toronto believe it can be determined by a mutation in genes known as BRCA1 and 2. Women with this mutation have up to an 80 per cent greater lifetime risk of developing breast cancer if they have also been taking the Pill.

They arrived at the theory after studying 1,311 pairs of women who had mutations in one or both of the genes. Half the women already had breast cancer, and half were healthy.

There seemed to be a few danger signs about Pill usage. Women who had used the Pill for five years, or those who used the Pill before the age of 30, or those who first used the Pill before 1975 (the generation of the Pill that had higher oestrogen content) had up to a 42 per cent higher risk of developing breast cancer compared with women with the mutation who had never taken the Pill.

So, if you know you have the mutation, what should you do? The researchers suggest that taking the Pill after the age of 30 doesn’t seem to increase your risk of breast cancer.

(Source: Journal of the American Medical Association, 2003; 289: 164).