Angelina Jolie reveals she had a double mastectomy

Brad Pitt has spoken of his partner's heroism, saying: "All I want is for her to have a long and healthy life, with myself and our children".

Angelina Jolie with her 'loving and supportive' partner Brad Pitt. Picture: AP

Not all breast cancer is caused by mutations in the BRCA1 gene that Jolie inherited from her mother. Dr Jo Morris, senior lecturer in the School of Cancer Sciences at the University of Birmingham, has written for us explaining just what BRCA1 is and why it matters.

We all have the BRCA1 gene, she explains, but in some cases - like Jolie's - it is broken, leading to a cell that grows where it shouldn't, causing cancer.

The chance that any one person has a mutation in this BRCA1 is thankfully rare. The prevalence of BRCA1 and BRCA2 ( BRCA1’s sister gene) mutation carriers in the general population is estimated at between 1 in 800 and 1 in 1000 and less than 10% of breast cancer is caused by changes in these genes.

Being at high risk is related to the number and age of affected family members and whether ovarian or male breast cancer is in the family. For most women, increasing age is the greatest risk factor for breast cancer. The great majority of women with a family history of breast cancer do not fall into a high-risk category and do not develop breast cancer and the majority of women with a relative with breast cancer are not at substantially increased risk of breast cancer themselves.

- www.telegraph.co.uk