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The presence of autoantibodies is considered to be a malfunctioning of the immune system. The immune system responds to the presence of antigens, which are unusual proteins or carbohydrates on the surfaces of invading organisms, by producing antibodies against these antigens. (Introduction to Immunology Part 2The antibodies then bind with the antigens, initiating a process leading to destruction of the organisms. During the process of its development, the immune system learns to distinguish self from non-self. For reasons not entirely clear, the immune system can develop antibodies against normal body constituents, such as proteins and nucleic acids,leading to diseases such as diabetes and lupus. 6 Cancer cells are produced by the body, and can present either novel proteins, or abnormally large amounts of normal proteins. The immune response to these proteins can also lead to the production of autoantibodies. There are several mechanisms by which cancer antigens can stimulate an immune response: gene activation or repression, gene mutation, and amplified expression of gene products (proteins). 5)
"There is no detection instrument that rivals the sensitivity and specificity of the immune system." This statement by Dr. Finn 2 sums up the attractiveness of using autoantibodies as a tool to detect cancer at its very earliest stages, when the number of cancer cells is very small. What progress is being made to develop this detection system? Prostate cancer Current screening for prostate cancer consists of a blood test for prostate-specific antigen (PSA), in conjunction with the older digital rectal examination. The PSA test has come under criticism, due to the large number of "false positives." False positives are high levels of PSA that should indicate the presence of cancer, but prove not to be the case. Researchers 1 isolated 22 autoantibodies associated with prostate cancer. These autoantibodies were tested against serum of patients with prostate cancer and control subjects without the cancer. Results indicated a specificity value of 88%, indicating the proportion of subjects correctly identified as being free of the disease. Results further showed a sensitivity value of 82%, indicating the proportion of patients correctly diagnosed a having prostate cancer. These results indicate that testing for a combination of prostate cancer autoantibodies would increase the screening sensitivity over PSA alone. Breast cancer p53 protein is known as the "guardian of the genome" and its levels rise dramatically in response to DNA damage. The p53 tumor suppressor gene High levels of p53 protein are normally only transient while it performs its role of either halting cell growth until the damaged DNA can be repaired, or initiating programmed cell death. When the p53 gene mutates, however, the resultant abnormal protein persists in the blood, leading to the formation of autoantibodies. Since mutated p53 genes are the most common mutated genes in cancers, great interest was shown in using the presence of p53 autoantibodies as a screening tool. Unfortunately, a large study 3involving 1006 patients with breast cancer found that "the presence or absence of p53 autoantibodies was not predictive of the presence or absence of recurrent disease." It appears that p53 autoantibodies occur in only about 15-20% of tumors, and even after the cancer is cured, p53 autoantibodies may persist due to other stimuli.6 Therefore, p53 autoantibody appears not to be useful as a screening tool. Go To Page: 1 2
The copyright of the article Detecting Cancer with Autoantibodies in Cancer Treatment is owned by David Olle. Permission to republish Detecting Cancer with Autoantibodies in print or online must be granted by the author in writing.
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