Immune cells in the body could be making cancer patients resistant to treatment. Dr Raowf Guirgis (National Cancer Institute)

The body's immune system could be making cancer patients resistant to the drugs which are trying to save their lives, according to scientists.

A study by Cancer Research UK has found that immune cells, called macrophages, are putting out chemicals that are acting as 'survival signals' to melanoma or skin cancer cells making them resistant to drugs.

During chemotherapy or radiotherapy, the patient's body becomes inflamed and produces more macrophages, and as a direct result, the 'survival signals', known as TNF alpha, also increase.

Once scientists blocked the macrophages' ability to make the signal, they found that the melanoma tumours became much smaller and easier to treat.

"This discovery shows that immune cells can actually help melanoma cells to survive. Particularly when patients are receiving treatment, the immune cells produce more of the survival signal, which makes treatment less effective," said study author Dr Claudia Wellbrock. "So combining standard treatment with immunotherapy at the same time could potentially provide more long-lasting and effective treatments to increase survival."

Melanoma is the most deadly form of skin cancer and particularly common among Caucasians. Around 13,300 people are diagnosed in the UK each year, with the rate increasing fivefold since the 1970s.

"Melanoma is particularly difficult to treat as many patients develop resistance to standard treatment within a few years. This research provides a key insight into why this is the case," said the study's co-author, Professor Richard Marais.

Scientists have already developed drugs to help combat the signals being produced by the macrophages and are hoping to use them in conjunction with standard treatments to find new ways of treating disease.