In a discovery that could lead to new treatments to prevent relapse of cancer, scientists have claimed to have uncovered how a small number of cancer cells escape from chemotherapy by hiding in a protective shield.

In a study of mice, biologists at the Massachusetts Institute of Technology (MIT) in Cambridge found that a few cancer cells hide inside the thymus, an organ where immune cells mature and escape the treatment.

While hiding there, they are bathed in growth factors that protect them from the drugs’ effects.

Those cells are likely the source of relapsed tumours, said Michael Hemann, MIT assistant professor of biology, who led the study.

Those drugs were originally developed to treat arthritis, and are now in clinical trials for that use.

According to the scientists, such a drug, when used in combination with traditional chemotherapy, can offer a one-two punch to eliminate residual cells and prevent cancer relapse.

“Successful cancer therapy needs to involve a component that kills tumour cells as well as a component that blocks pro-survival signals,” said Hemann.

“Current cancer therapies fail to target this survival response.”

The exact mechanism is not known, but the researchers believe that chemotherapy-induced DNA damage provokes those blood-vessel cells to launch a stress response that is normally intended to protect progenitor cells immature cells that can become different types of blood cells.

“In response to environmental stress, the hardwired response is to protect privileged cells in that area, that is progenitor cells,” said Hemann.

“These pathways are being coopted by tumor cells, in response to the frontline cancer therapies that we use.”

The discovery marks the first time scientists have seen a protective signal evoked by chemotherapy in the area surrounding the tumour, known as the tumour microenvironment.

“It’s completely unexpected that drugs would promote a survival response,” said Hemann.

While the MIT researchers observed this protective effect only in the thymus, they believe there may be other protected areas where tumour cells hide, such as the bone marrow.

This finding could help explain why tumours that have spread to other parts of the body before detection are more resistant to frontline chemotherapy, they added.