The researchers used a technique known as ChIP-sequencing to look at how the FOXA1 protein interacted with the DNA. This revealed that FOXA1 attached to the DNA at almost all the same points as the oestrogen receptors did and that it was essential for them to be able to make contact with the DNA.

Breast cancer is the most common cancer in the UK. Almost 45,700 women are diagnosed with the disease each year, of which about 30,000 women have hormone-sensitive breast cancers.

Dr Lesley Walker, director of cancer information at Cancer Research UK, said: "We know that some women with breast cancer stop responding to tamoxifen, making them more prone to relapsing. This important discovery could one day lead to new drugs that help improve the outcome for these patients.

"Cancer Research UK was involved in some of the key early clinical trials of tamoxifen as a breast cancer treatment in the 1980's and 90's, which have played a huge part in the vastly improved survival rates seen today."

Source: Cancer Research UK