Your immune system is continuously monitoring the body for cancerous cells. Each of us have probably had A cancerous cell hundreds of times. In order for the ca

Your immune system is continuously monitoring the body for cancerous cells. Each of us have probably had A cancerous cell hundreds of times. In order for the cancer to continue to grow, though, it needs a constellation of mutations to impede the immune response, among other things. Essentially, it's a race between a proto-tumor accreting more mutations, and the immune system finding and destroying it.