When it comes to cancer treatment, many doctors use chemotherapy to stop or slow the growth of a tumor. However, new research presented in the journal Nature suggests that certain types of chemo that aim to put cancers into a so-called sleep state may not be as effective as once thought, Medical News Today reports

The Vienna-based study focused on a cancer-fighting phenomenon known as senescence, in which cancer cells essentially go to sleep after chemotherapy is used to damage their DNA beyond repair (instead of killing the cancer outright, like other types of chemo). The process was discovered more than 50 years ago and until recently was thought to induce a state of irreversible growth arrest for malignant tumors, meaning that the cells remain in place but stop growing.

But now scientists say they may have discovered why in certain cases, this sleep state may actually provide a fertile area for cancer stem cells to grow in the body — which could pave the way for tumors to metastasize, or grow back and spread.

For the study, originally published in the journal Frontiers in Oncology, researchers examined lymphoma cells from mice (lymphoma is a type of cancer that affects white blood cells). As expected, when researchers initially used cancer drugs to induce senescence on these cells, they stopped dividing. 

However, researchers say that over time, these senescent cancer cells started to resemble cancer stem cells, a phenomenon known as stemness. It is thought that this stemness may have the potential to promote cancer in the body — specifically by expressing genes known as p21 and p24 that are vital for maintaining stem cell functions.

In fact, later, when the research team released these cancer cells from their senescent state using genetic manipulation, they started multiplying quickly within a few days. Study authors noted that this suggests that very few new cells are needed to kick-start the development of new cancer tumors in the body and that cancer cells may in fact be able to escape senescence in certain cases. 

“When cancer cells escape from senescence, they have enhanced capability to drive tumor growth — a finding that has potential clinical implications,” the Nature summary of the report concludes. However, researchers say far more research is needed on non–genetically modified cancer cells to help clarify and confirm the findings.