The body fortunately has an immune system that helps to protect the body against various types of infections, certain illnesses, and cancer. There are new treatments available that allow the body to fight cancer cells.
One article (1) discussed the immune system and cancer, particularly what the immune system does to fight off cancer cells. For example, the immune system can scavenge for abnormal, cancerous cells and get rid of them, much in the same way that the immune system fights infection.
The article noted that the immune system may be able to fight cancer but that chemotherapy treatments often weaken the immune system, and cancer itself can cause the immune system to be dysfunctional. When cancer has spread to the bone marrow, it crowds out normal bone marrow cells and the immune system is weakened as a result of this. Many cancer treatments can also weaken the immune system but this is usually a temporary phenomenon.
Source: 1.The immune system and cancer. http://www.cancerresearchuk.org/about-cancer/what-is-cancer/body-systems-and-cancer/the-immune-system-and-cancer#mIvVal5JJYxC5Ym1.99 Accessed 8/1/16.
Dr. Adem Gunes