Immune surveillance is the idea that certain white blood cells of our immune system are continually and constantly keeping a watchful eye for any abnormal cells that might develop in our body. And these abnormal cells might develop as a result of some type of pathogenic infection or they might develop as a result of some type of carcinogenic. So when healthy cells are exposed to carcinogens such as chemical agents, pathogenic agents or radiation for example UV or X ray radiation the healthy cells can essentially become cancer cells. Now, how exactly does a healthy cell become a cancer cell? Well, these carcinogens essentially affect the DNA molecules within our healthy cells. And when we develop a mutation in our DNA molecule we change the sequence of nucleotides on that DNA and that ultimately codes for different proteins and that can influence the functionality of the cell.