Blocking a certain type of immune cells holds the key to treat melanoma - a deadly form of skin cancer, according to new research.

British scientists have found that chemical signals produced by a type of immune cells, called macrophages, also act as a "survival signal" for melanoma cells.

When researchers blocked the macrophages' ability to make this signal - called TNF alpha - melanoma tumours were much smaller and easier to treat.

"This discovery shows that immune cells can actually help melanoma cells to survive," said Claudia Wellbrock, a cancer research scientist at University of Manchester and member of the Manchester Cancer Research Centre.

During the treatment of patients, immune cells produce more of the survival signal which makes treatment less effective.

"Combining standard treatment with immunotherapy could potentially provide long-lasting and effective treatments to increase survival," Wellbrock added.

When melanoma patients are given chemotherapy or radiotherapy it causes inflammation, increasing the number of macrophages in the body - and raising the levels of TNF alpha.

Drugs which block this "survival signal" have already been developed and using these along with standard treatment may be a promising new approach for melanoma patients, researchers concluded in the journal Cancer Discovery.