Tumors can produce pyrogens, cause an infection that produces pyrogens, or interfere with the normal functioning of the hypothalamus. Cancer treatments can directly cause fever or weaken the immune system, making it more vulnerable to inflammation and infections. A fever is usually caused by an infection, but other causes may include inflammation, reactions to medications, or tumor growth. Sometimes, the cause may not be known or it may not be easy to find. In an infection, a fever is the result of the body trying to fight invading germs.
Fever is an important natural defense against germs. It's not really understood why certain types of cancer cause fever and others don't. It is thought that some types of cancer can produce toxins that cause fever. People being treated for cancer have a higher risk of getting infections because cancer treatment can cause neutropenia, a condition in which there are fewer white blood cells than normal to help fight infections. The American Cancer Society offers programs and services to help you during and after cancer treatment.
Other authors have observed similar results with naproxen and, although it is not pathognomic for cancer fever, a challenge test with naproxen may be useful in reducing the cause of undiagnosed fever when cancer is suspected. Another area where attention should be focused in a febrile patient with suspected cancer is the skin, since metastatic renal cell or bronchogenic cancer can compromise the integument, as can leukemia (“leukemia cutis”).