Description

Cancer can weaken the immune system by spreading into the bone marrow. The bone marrow makes blood cells that help to fight infection. This happens most often in leukaemia or lymphoma, but it can happen with other cancers too. The cancer can stop the bone marrow from making so many blood cells. Cancer treatments that are more likely to weaken the immune system are chemotherapy, targeted cancer drugs, radiotherapy and high dose of steroids. After a cell becomes cancerous, the immune system is often able to recognize it as abnormal and destroy it before it replicates or spreads. The cancerous cells may be completely eliminated, in which case the cancer never appears. Certain cancers are more likely to progress in people whose immune system is altered or impaired, as in people with AIDS, people receiving medications that suppress the immune system, people with certain autoimmune disorders, and older people, in whom the immune system works less well than in younger people. Cancers that are more common with a weakened immune system include melanoma, kidney cancer, and lymphoma. Doctors are not sure why certain other cancers, such as cancers of the lung, breast, prostate and colon, are not more common in people with a weakened immune system. An antigen is a foreign substance recognized and targeted for destruction by the body’s immune system. Antigens are found on the surface of all cells, but normally the immune system does not react to a person’s own cells. When a cell becomes cancerous, new antigens are unfamiliar to the immune system which appears on the cell surface. The immune system may regard these new antigens, called tumor antigens, as foreign and may be able to contain or destroy the cancerous cells. This is the mechanism by which the body destroys abnormal cells and is often able to destroy cancerous cells before they can become established. However, even a fully functioning immune system cannot always destroy all cancerous cells. And, once cancerous cells reproduce and form a large mass of cancerous cells (a cancerous tumor), the body’s immune system may be overwhelmed.