Scientists have pinpointed a molecular mechanism in mice that helps skin cancer cells confound the animal's immune system, according to a study.
The discovery, if duplicated in humans, could one day lead to drug treatments that block this mechanism, and thus the cancer's growth, the study's authors report.
In experiments on mice, researchers showed for the first time that a protein called interferon-gamma (IFN-gamma) plays a key role in the spread of melanoma, a notoriously aggressive form of cancer resistant to standard chemotherapy.
The same kind of ultraviolet radiation that leads to sunburn caused white blood cells to infiltrate the skin of the mice, says Glenn Merlino, a scientist at the US National Cancer Institute and the main architect of the study.
The white blood cells, in turn, "can produce IFN-gamma. We believe that IFN-gamma can promote melanoma in our model system, and perhaps in people," he says.
Injecting the mice with antibodies that block IFN-gamma interrupted this signalling process, effectively reducing the risk of UV-induced skin cancer, the researchers found.
"We are trying to develop inhibitors that are more practical than antibodies, a small molecule, for example," says Merlino.
Ideally, such a treatment would mean that someone exposed to large doses of UV radiation could escape the potentially lethal threat of skin cancer.
"But we would never encourage intense sunbathing, even if such a treatment were available," cautions Merlino.
Cases of cutaneous malignant melanoma are increasing faster than any other type of cancer.
In 2000, more than 200,000 cases of melanoma were diagnosed and there were 65,000 melanoma-associated deaths, according to the World Health Organisation (WHO).
Upending assumptions about interferons
The findings, reported in the journal Nature, could upend assumptions about the relationship between interferon proteins and cancer, say the study's researchers.
Up to now, interferons were thought to impede the formation of cancer tumours. One in particular, interferon-alpha, has been widely used to treat melanoma, both as a first-line drug and an adjutant.
Earlier research has raised doubts as to effectiveness of the treatment, which also has serious side effects.
The highest recorded incidence of melanoma is in Australia, where the annual rates for women are 10 times the rate in Europe and more 20 times for men.
The main risk factors are high exposure to the Sun and other UV sources such as sun-beds, along with genetic factors.
The disease is far more common among people with a pale complexion, blue eyes, and red or fair hair.