Everyone has BRCA1 and BRCA2 genes, but mutations in these – which can be inherited – increase the risk of breast and ovarian cancer.

Researchers at the University of Cambridge have now created the world’s largest catalogue of human breast cells, which has revealed early cell changes in healthy carriers of BRCA1 and BRCA2 gene mutations.

The study found that the immune cells in breast tissue of healthy women carrying BRCA1 or BRCA2 gene mutations show signs of malfunction known as “exhaustion”. This suggests that the immune cells can’t clear out damaged breast cells, which may eventually develop into cancer.

This is the first time that “exhausted” immune cells have been reported in non-cancerous breast tissues – normally these cells are only found in late-stage tumours.

The results raise the possibility of an exciting medical advance – using existing immunotherapy drugs early to prevent breast cancer ever developing in carriers of BRCA1 and BRCA2 gene mutations.

“Our results suggest that in carriers of BRCA mutations, the immune system is failing to kill off damaged breast cells, which in turn seem to be working to keep these immune cells at bay,” said Professor Walid Khaled of Cambridge University and senior author of the report.

He added: “We’re very excited about this discovery because it opens up potential for a preventative treatment other than surgery for carriers of BRCA breast cancer gene mutations.

“Drugs already exist that can ­overcome this block in immune cell function, but so far, they’ve only been approved for late-stage disease. No one has really considered using them in a preventative way before.”

Risk-reducing surgery, in which the breasts are removed, is offered to women at increased risk of breast cancer, but this can be a difficult decision for young women to make, and can have a significant effect on body image and sexual relationships.

“The best way to prevent breast cancer is to really understand how it develops in the first place. Then we can identify these early changes and intervene,” says Prof Khaled.

Using samples of healthy breast tissue collected from 55 women across a range of ages, the researchers
catalogued over 800,000 cells – including all the different types of breast cell.

The resulting Human Breast Cell Atlas is now available as a resource for other researchers to use and add to. It contains huge amounts of information on other risk factors for breast cancer including body mass index (BMI), menopausal status, contraceptive use and alcohol consumption.