Radiation therapy for cancer patients in some cases could be doing more harm than good.
Researchers in the US have found radiation used to kill cancerous cells depresses the body's immune response in the area around the tumour, allowing surviving cancerous cells to multiply with little resistance.
Langerhans cells, found in the skin, can resist the damaging effects of radiation.
"In a series of experiments, the researchers show that Langerhans cells take up cell debris triggered by irradiation, including tumour proteins, and migrate to draining lymph nodes," according to scientists at New York's Icahn School of Medicine.
Once at the lymph nodes, the Langerhans cells activate T cells, which are normally used to end the body's immune response.
"These regulatory T cells prevent the activation of anti-tumour immune responses and thereby promote resistance among any tumour cells that survived the radiation treatment."
Writing in journal Nature Immunology, cancer experts Laurence Zitvogel and Guido Kroemer say the findings should make oncologists think twice about using radiation therapy on large areas of the skin, so a minimum number of Langerhans cells are triggered into action.
"Alternatively, if skin exposure is unavoidable, radiotherapy should be accompanied by treatments that keep T cells in check," they argue.
The findings come the same week New Zealand doctors have called for a breakthrough treatment for melanoma to be funded.