There is strong evidence to suggest that the immune system plays a role in preventing cancerous tumors. However research also suggests that the tumors may evade the immune system's defenses.

In a set of experiments involving mice which lacked working lymphocytes, Schreiber and his colleagues at Washington University and Memorial Sloan-Keterring Cancer Center in New York demonstrated that the immune system does appear to play some role in the prevention of the growth of tumors.

Tumors developed earlier and more frequently in mice without lymphocytes than in mice with normal immune systems. Although the research confirms that the immune system is involved in suppressing tumors, its precise role is different than previously thought.

The immune system destroys cancerous cells when it recognizes proteins or other markers expressed by tumor cells. However tumor cells can also develop resistance to the attacks of the immune system just as bacteria can towards antibiotics. Tumor cells may evade the immune system's defenses by no longer expressing the proteins that the immune system uses to identify tumors. This explains why some tumors transferred from mice without immune systems continued to grow when they were placed in healthy mice, as reported in Nature (2001; 410:1107-1111).

Up till the mid to late 1970s, Schreiber noted that many cancer scientists suspected that the immune system played a role in preventing tumors by identifying and destroying cells as they began the transformation into cancer. However this idea known as immunosurveillance, suffered a major blow when an experiment in the late 1970s showed that mice with damaged immune systems did not develop tumors any more frequently than normal mice.

But there was a major flaw in these experiments, as the immune systems of the mice were not completely eliminated. The mice did not completely lack immune-system cells called lymphocytes as had been thought.

Information provided is courtesy of and compiled by the Academy of Anti-aging Research staffs, editors, and other reports.
 

There is little doubt that weak immunity is an invitation for cancerous cells to proliferate. A strong immune system is one of the key components of longevity and cancer prevention. Anti-oxidants such as vitamin C strengthen the immune system. Adequate rest, proper diet, stress free life, and exercise all go towards enhancing our immune mechanism and should not be overlooked.