Aspirin may be able to boost the effectiveness of cancer medicines that improves the immune system. Immunotherapy lets the body's own defenses fight cancer. Scientists at the Francis Crick Institute have published a study suggesting aspirin may prevent tumors from hiding from the immune system. Cancer Research UK said it could be a simple way of improving treatment. The team showed that skin, breast and bowel cancer cells were producing high levels of a chemical, called prostaglandin E2, that could dampen down the immune response - effectively letting a tumor hide.