A new two-in-one drug combining Herceptin (trastuzumab) with chemotherapy has been found to keep women’s breast cancers at bay.

A new clinical trial has found that guiding chemotherapy to a tumour by attaching it to the antibody-based target drug Herceptin is effective at treating women with breast cancer who have no other treatment options.

In the trial, women with HER2-positive breast cancer lived for 7.6 months after starting the treatment with no disease progression, whilst those with lower HER2 levels had progression-free survival of 4.9 months, showing that the drug extended life for patients who have run out of other treatment options.

The treatment was effective in women with HER2-positive breast cancer who had stopped responding to existing drugs, and as well as being effective in women with high HER2 levels in their tumour, it was also active in a subset of women with lower levels of the HER2 protein who currently have no treatment options.

The antibody acts as a guide for the attached drug, detecting the HER2 protein on the surface of the cancer cells. Once these two drugs – attached by a ‘linker’ to form the antibody drug conjugate – are internalised into the cancer cell, the linker is broken by enzymes within the cell to release the cytotoxic drug, resulting in DNA damage to the cancer cell. This approach allows the drug to be delivered directly to the target cancer cells.

As this method selectively targets the cancer cells, it minimises the damage done to the surrounding healthy cells, reducing toxicity and side effects in the patient.

First author professor Udai Banerji, deputy director of the drug development unit at The Institute of Cancer Research, said that “The approach used in this study of combining the antibody and drug is a highly successful way of targeting tumours. With the antibody acting as a guide to find and target the cancer, the duocarmazine drug can be released directly to the tumour cells, destroying them whilst minimising the damage to surrounding healthy cells.”

“Trastuzumab duocarmazine has shown promising anti-tumour activity in breast cancer patients with varying levels of the cancer-driving HER2 protein. As these cancers often develop resistance to the current standard of care, this treatment could be extend the lives of patients who have otherwise run out of options.”

The study was published in The Lancet Oncology and funded by Synthon Biopharmaceuticals.