New drug slows or stops an aggressive type of breast cancer in 76% of cases

The new drug is an immunoconjugate, i.e. an antibody - a protein secreted by B lymphocytes in the blood to fight a virus or bacterial infection affecting the body - that has chemotherapy molecules attached to it. It acts like a 'Trojan horse'. When it is administered, it travels through the blood to the tumour cells that have a receptor called HER2. HER2 is the gateway through which the drug enters the tumour cell undetected and, once inside, releases the chemotherapy that transports and destroys the tumour cell. “This drug stays in the tumour microenvironment and is able to attack neighbouring cells as well, even if they do not have HER2, which is known as the bystander effect, a consequence that does not occur in other treatments of this type and which is very positive, even though some healthy cells may be damaged," explains Dr Cortés.

The trial involved 524 women with this type of breast cancer, being treated at 169 centres in 15 countries between 2018 and 2020. “There has never been a drug which has demonstrated as much benefit as this one. We could be looking at the most active medication ever in the history of breast cancer,” says Dr Cortés. He says the drug could cure the illness in some patients or, at least, increase the chances of it being treated as a chronic condition.

However, like all treatments, it is not without toxicity. One of its adverse effects is drug-related interstitial lung disease/pneumonitis (lung inflammation). Rates of this related to T-Dxd were 10.5% versus 1.9% with TDM-1, but close monitoring or follow-up of patients treated with T-Dxd allows for early detection, treatment and control of this effect in the vast majority of patients.

The drug is already approved and available for use in Spain, although price negotiations with the Ministry of Health have not yet been finalised. "We are facing a real revolution. These 'Trojan horses' are going to be one of the most important lines of research in the future. There are already studies showing fascinating results," says Dr Cortés.