Researcchers have shown that skin, breast and bowel cancer cells often produce large amounts of prostaglandin E2 (PGE2). This molecule dampens down the immune system's normal response to attack faulty cells, which helps cancer to hide. It is a trick that allows the tumor to thrive and may explain why some immunotherapy treatments have not been as effective as hoped.

Aspirin is part of a group of molecules called COX inhibitors, which stop the production of PGE2 and help reawaken the immune system. Combining immunotherapy with aspirin or other COX inhibitors substantially slowed bowel and melanoma skin cancer growth in mice, compared to immunotherapy alone.

PGE2 acts on many different cells in our body, and this study suggests that one of these actions is to tell our immune system to ignore cancer cells. Once you stop the cancer cells from producing it, the immune system switches back to 'kill mode' and attacks the tumor.

This research was carried out in mice so there is still some way to go before we will see patients being given COX inhibitors as part of their treatment. But it's an exciting finding that could offer a simple way to dramatically improve the response to treatment in a range of cancers.

http://www.cell.com/cell/abstract/S0092-8674(15)01028-4