Combining immunotherapies could benefit some aggressive breast cancers

Using two immunotherapy drugs together could help treat some patients with an aggressive form of breast cancer, according to an Australian study. 

Researchers at Walter and Eliza Hall Institute and Peter MacCallum Cancer Centre in Melbourne found that combining the immune-boosting drugs with chemotherapy increased survival in mice with a type of breast cancer. 

Although it’s too early to say whether this will work in people, study author Dr Daniel Gray said the results offer “compelling evidence” to test out the combination in clinical trials for women with this disease.

“The study highlights a group of patients that are most likely to benefit from drugs boosting the immune system,” said Professor Aymen Al-Shamkhani, a Cancer Research UK expert on immunotherapy from the University of Southampton. 

These patients carry faults in a DNA-fixing gene known as BRCA1. The type of breast cancer is also an aggressive form known as ‘triple-negative breast cancer’ (TNBC), as the tumour cells also lack 3 different hormone-sensing molecules on their surface. 

Effective treatments that specifically target these molecules in other types of breast cancer are already widely used. However, the development of such targeted therapies for TNBC has been slow. 

For this latest study, scientists tested out a different approach: targeting immune-dampening molecules known as ‘checkpoints’. These normally prevent the immune system from going into overdrive. But in people with cancer they can stop immune cells from effectively attacking tumours. Drugs that block these checkpoints – called immunotherapies – release the immune system’s brakes and enhance its cancer-fighting abilities. 

Looking at mice with this type of breast cancer, the researchers found that using molecules to block two different checkpoints, combined with a chemotherapy drug, boosted the animals’ immune response against the tumour. This approach also slowed down their tumour growth and improved survival. The results are published in the journal Science Translational Medicine. 

“This study suggests a possible role for combining two immunotherapy drugs with chemotherapy in the treatment of some of patients with TNBC that have faulty BRCA1 genes,” said Dr Adel Samson, a Cancer Research UK immunotherapy expert from the University of Leeds.

“This is obviously welcome news, as TNBC has a poor outlook, although this treatment strategy could cause serious side effects. These treatments should therefore be first tested in carefully designed early clinical trials.”

Professor Al-Shamkhani also echoed the need for further research.

“The combination of checkpoint blockers used in this study has proven to be highly effective in the treatment of some patients with advanced melanoma,” he said. “This study therefore backs up the rationale for clinical testing of these checkpoint blockers as a treatment for these women.”