A Japanese study conducted on fruit flies found that immune cells attacking cancer cells release signals that can actually cause tumours to grow more aggressively. 

Researchers at Nagoya University found that immune cells, when absorbing dying cancer cells, release signals that make the remaining cancer cells grow faster. This process, known as phagocytosis, normally helps the body clear damaged or infected cells. But in this case, it also triggered the release of inflammatory proteins, which then activated growth signals in the surviving cancer cells.  

“We used genetically modified fruit flies to study cancer because their immune system is similar to ours, and they offer a powerful model system for research in the laboratory,” said Eri Hirooka, a Ph.D. student at Nagoya University and lead author. 

To better understand this process, the team used genetic tools to switch specific genes on and off and change the levels of certain proteins in the fruit flies. By turning off genes needed for phagocytosis, the researchers reduced the ability of macrophages to absorb dying cancer cells. As a result, tumour growth was reduced. The researchers linked this effect to a protein called Upd3, which is similar to IL-6, a protein found in human cancer.  

Shizue Ohsawa, senior author of the study, said: “Because the molecular pathways between fruit flies and humans are evolutionarily preserved, understanding these mechanisms could explain why some cancers with high cell death rates can still grow aggressively and lead to improved treatments.”  

The study, published in the journal Current Biology, suggests that boosting the immune system’s ability to clear cancer cells may not always have the expected benefit, providing new insights on future therapies.