Scientists have identified a molecule that can help treat breast cancer, giving hope to patients who have become resistant to traditional therapies.

The first-in-class molecule shuts down oestrogen-sensitive breast cancer in a new way, researchers said.

First-in-class drugs are those that operate via a unique mechanism, such as a molecule that targets a protein on the oestrogen receptor of cancer cells.

The new potential drug offers hope for patients whose breast cancer has become resistant to traditional therapies.

“This is a fundamentally different, new class of agents for oestrogen-receptor-positive breast cancer,” said Ganesh Raj, professor at the University of Texas Southwestern (UT Southwestern) Simmons Cancer Center.

“Its unique mechanism of action overcomes the limitations of current therapies,” Raj said.

More than 80 per cent of breast cancers are found to be oestrogen-sensitive, researchers said.

These cancers can be sometimes treated with hormone therapy, such as tamoxifen, but as many as a third of these cancers eventually become resistant to that treatment, they said.

The new compound is a potential highly effective, next-line treatment.

Traditional hormonal drugs, such as tamoxifen, work by binding to a molecule called the oestrogen receptor in cancer cells, preventing oestrogen from binding to the receptor, a necessary step for cancer cells to multiply.

However, estrogen receptors can mutate and change their shape over time so that the treatment drug no longer fits neatly with the receptor. When this happens, the cancer cells start multiplying again.

“There has been intense interest in developing drugs that block the ability of the oestrogen receptor – the prime target in most breast cancers – from interacting with the co-regulator proteins that cause a tumour’s growth,” said David Mangelsdorf, professor at UT Southwestern.

“Blocking such “protein-protein interactions” has been a dream of cancer researchers for decades.

The new drug, recently approved by the Food and Drug Administration, works by blocking other molecules, called co-factors, that also must attach to the receptor for cancer cells to multiply.