Mesothelioma Symptoms - Malignant Growth
Epidemiologic Studies (cont.)
The Canadian Breast Cancer Fluoroscopy Study13 reports the observations of the mortality from breast cancer in a cohort of 31,710 women who had been examined by multiple fluoroscopy between 1930 and 1952. The observed rates of mortality are related to breast radiation doses and presented only in tabular form. The authors compare linear and linear-quadratic dose-response models fit to the data and conclude, "that the most appropriate form of dose-response relations is a simple linear one, with different slopes for Nova Scotia and the other provinces." On the basis of this linear model that includes only non-significant data and excludes the data with the highest confidence limits , the authors predict the lifetime excess risk of death from breast cancer after a single exposure at age 30 to 1 cGy(1r) to be approximately 60 per million women or 900 per million women exposed to 15 cGy. The observed data, however, demonstrate with high statistical confidence, a reduction of the relative risk of breast cancer to 0.66 (P=0.05) at 15 cGy and 0.85 (P=0.32) at 25 cGy.
The second author, in his 1996 revision of this study, removed this highly significant contradiction of the LNT hypothesis by lumping all low-dose data into a single 1-49 cGy category.14 The study actually predicts that a dose of 15 cGy would be associated with 7,000 fewer deaths in these million women. Lauriston S. Taylor, past president of the NCRP, considered application of LNT theory for calculations of collective dose as, "deeply immoral uses of our scientific heritage"15. METABOLIC AND RADIATION DNA DAMAGE CONTROL.
During the past decade rapid advances in our knowledge of molecular biology and cell function enable us to understand why low-dose radiation is associated with positive health effects in contrast to the carcinogenic effect of high-dose radiation. Our understanding is based upon current, cellular molecular biology observations. Estimates are based on published data and recent personal communications: * Two to three percent of all metabolized oxygen is converted to free radicals (reactive oxygen species),16 10E10/cell/d, that produce about 10E6 DNA oxidative adducts/cell/d.7, 8 These include about 0.5 double strand breaks/cell/d.17 In addition, a relatively small number of metabolic DNA alterations are produced by DNA replication and thermal instability.19
By comparison, 1 cGy low LET radiation produces 20 DNA oxidative adducts/cell that include an average of 0.4 double strand breaks/cell.18,19 * Over eons of time, as multicellular animals developed and metabolized oxygen, a complex DNA damage-control biosystem evolved .17 The damage corresponding to 10E10 free radicals/cell/d is largely prevented by antioxidants that scavenge approximately 99% of these free radicals. The resultant 10E6 DNA oxidative adducts/cell/d are reduced by enzymatic repair to about 10E2 mis/unrepaired DNA alterations/cell/d.
Apoptosis, differentiation, necrosis, and the immune system remove approximately 99% of these mis/unrepaired DNA alterations so that an average of 1 mutation/cell/d (possibly up to 2-3) accumulates during the lifetime of a stem cell to decrease DNA damage-control capability with associated aging and malignant growth .17 Cancer increases as the third to fifth power of age. This remarkably efficient biosystem prevents precocious aging and malignancy unless impaired by genetic defects, or damaged by high doses of radiation or other toxic agents. 9, 16-19, 22-33
* How does background radiation add to the metabolic accumulation of mutations? A much larger fraction of double strand breaks occurs in DNA oxidative adducts produced by radiation than in those produced by metabolism (2x10E-2 vs 5x10E -7).17,21 The mis/unrepaired fraction of these double strand breaks is also much larger than that of other metabolic DNA oxidative adducts (10E-1 vs 10E-4). Nevertheless, the number of metabolic DNA oxidative adducts (10E6/cell/d) is so much greater than the number of oxidative adducts from low LET background of 0.1 cGy/y (5x10 -3/cell/d), that an average of only 10E -7 radiation mutation/cell/d is added to 1 metabolic mutation/cell/d .17
Mesothelioma Symptoms vary dependent on the type of mesothelioma one is suffering from. Because of the latency period associated with the disease, early-stage malignant mesothelioma can often be asymptomatic.