werner@aecom.UUCP (Craig Werner) (07/24/85)
<> Subject: The Immune System and Cancer. In response to an article I pointed out that described the (albeitly limited) successes of Chemotherapy for Cancer, Thomas Stanions pointed out that this was only treating the symptoms and that the underlying CAUSE of cancer was a weak immune system. At the time, I did not respond. I could have said 'Well, it just ain't so.' However, that would have left me open to the retort, "Well do you have proof?" Good Question. Can one disprove the assertion that the development of cancer is caused by a weak immune system? After several months of thought, I can say "Yes, it can be done." (I even sent a copy of this for his perusal prior to my posting it.) Point 1: In order for anything to be attacked by the immune system, it must be recognized as 'foreign.'[*] Despite, years of searching, only three tumors (out of thousands) have been found that display foreign characteristics (called antigens). One is Choriocarcinoma, a cancer of the placenta, and it is recognized as foreign because it contains genes from the father; another is Burkitt's Lymphoma, which only occurs in cells that have been previously infected by Epstein-Barr Virus. In both cases, the tumors (20 years ago almost totally fatal) can be cured more than 95% of the time by a short round of chemotherapy, which slows the tumor down enough for the immune system to take care of it (as it would reject a graft or fight an infection, respectively). The third case, Colon cancer, the antigen found there, although not found in normal gut, is actually an embryonic antigen (i.e., it was there before birth and dissapeared) so is not recognized as foreign, and hence not attacked. The other two cancers, incidentally, almost never occur in the USA. * [It would take too long for me to adequately describe what 'foreign' entails. A definition for those who understand protein structure would be 'anything which presents a unique three-dimensional structure not normally encountered within the body' would capture the essence of 'foreigness.'] Objection 1: True, but could it be that the reason that no cancer has been found that the immune system can attack is because all the ones that the immune system could attack were killed early, and hence were never detected. This is unfortunately true (but for the researcher, intriguing), and illustrates the fact that the absence of positive proof does not constitute negative proof. [Perhaps someone should tell that to the Creationists, oh, well, nevermind.] Well, can the thesis that a weak immune system is responsible for cancer be disproven directly? Yes, it can. Point 2: The definitive experiment would be to weaken people's immune system and see if they developed cancer a few years down the line. Obviously, this cannot be done. It is not only impractical, but extremely unethical, and I doubt if one could get any volunteers for it anyway. However, there are two groups of people for whom this has already been one, one by nature, and another by medicine. I am referring to the 11,000+ people who have contracted AIDS (Acquired Immune Deficiency Syndrome), and to those who have received Kidney (or other organ) and have to be artificially immunosuppressed to keep from rejected the organ. The question then to ask is "Do these people die of Cancer more often than the population at large?" In the case of the AIDS population, the answer is that there are two relatively rare cancers that appear very frequently, one is Kaposi's Sarcoma, the other is another form of lymphoma. (But these are rare cancers - to give an idea, North Central Bronx Hospital has 5 cases of Kaposi's in the 25 years prior to 1980. They now get that many, all in AIDS patients, in a month.) Both of these only occur in certain, not all AIDS risk groups, so it could be that they are not a result of a weak immune system per se, but may be virally transmitted, like Burkitt's Lymphoma. As far as the Transplant patients go, I do not know of any increased risk of cancer among people receiving organ transplants. (It may actually be lower, only because they are more apt to die of complications relating to the earlier organ failure that required the transplant in the first place.) So there you have it, indirect but as near as can be definitive disproof of the theory that a weak immune system is responsible for cancer, or I should say, most cancer. [Further note: the working definition of a cured cancer is "Disease free survival for a period of five years following cessation of therapy, or if death occurs by a non-related cause (an accident, say), absence of tumor at post-mortem exam." Despite the non-feeling tone of the definition, it is the only OBJECTIVE way of evaluating survival.] -- Craig Werner !philabs!aecom!werner "The world is just a straight man for you sometimes"