Asbestos

Although many carcinogens have been well studied, particularly organic chemicals. Asbestos, while not being well studied appears to be a new type of carcinogen, that of particulate. Asbestos and other mineral fibers are carcinogenic to humans and animals but differ from many carcinogens in that they do not induce gene mutations. Evidence exists that asbestos is a complete carcinogen, an initiator and a promoter. Although asbestos is inactive as a gene mutagen, there is now clear evidence that it induces chromosomal mutations. Much the same as is discussed in our test on page 199, “The presence of these solid bodies creates the conditions for the transformation of normal…cells to malignancies.” From studies reported in the late 1960's and early 1970's, the chemical composition and crystallographic characteristics of asbestos are not now considered to be relevant to the carcinogenic potential of asbestos fibers. The major properties determining carcinogenic potential of asbestos fibers are their size and shape. The chemical composition has minimal relevance. It is when the cell attempts to “eat” the asbestos fiber through a process called phagocytosis that the long thin fibers essentially stab the cell, compromising the cell membranes ability to regulate calcium levels that are required for proper cellular reproduction. The presence of an inward leakage pathway for calcium caused by the presence of an asbestos fiber penetrating the cell's membrane is capable of both initiating the cell division cycle in a resting cell, and severely interfering with subsequent, calcium requiring reactions and programmed changes. Should the cell be unable to control this up-and-down progression of its internal calcium ion concentration, it would suffer from many unplanned and uncoordinated events which would be triggered out of sequence. Damage at the chromosomal level would be inevitable.
These studies of HOW asbestos induces mutations and hence cancer in cells were done in the laboratory of course. The actual human studies could very likely be biased due to the fact that only those individuals actually exposed to asbestos could develop asbestos induced cancer. Typically the only way to be exposed to asbestos is through industrial settings where asbestos is only one of many substances the workers are exposed to. Confounding, while similar to bias could also be at play in cancer development. What if some other factor is associated with the asbestos exposure? For example cutting fluid in brake manufacturing or tile cutting. Another factor that must be considered when studying asbestos as a possible carcinogen, in-vivo, is the limited sample size. There are only so many people exposed to asbestos that develop cancer where other factors can be ruled out.

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1567531
http://209.85.173.132/search?q=cache:r8uvcMWbPQkJ:jhguth1942.tripod.com/sitebuildercontent/sitebuilderfiles/Mechanism_of_Asbestos_Carcinogenesis.rtf+asbestos+carcinogen&cd=11&hl=en&ct=clnk&gl=us
http://www.asbestos.net/medical-glossary/carcinogenic.html
http://www.epa.gov/ttn/atw/hlthef/asbestos.html