Asbestos that has long been associated with mesothelioma and lung cancer has now been found to cause laryngeal malignancies as well .
The Indian Institute of Medicine revealed this finding in its report. In addition IOM also concluded that there was 'suggestive but not sufficient' evidence to point out conclude mineral fibers as a cause of pharyngeal, colorectal and stomach cancer. However there was insufficient evidence to relate asbestos to esophageal cancer.
The IOM, which is quasi-governmental institute, was set upon the task to 'comprehensively review, evaluate, and summarize the peer-reviewed scientific and medical literature' on asbestos and the five forms of cancer by the US senate. A debate on legislation to create a $140 billion asbestos-injury compensation fund provoked this study.
The multidisciplinary research committee of the IOM found 35 cohort studies and 15-case-control studies, which analyzed the link between asbestos and cancer of the larynx.
The cohort studies conducted their studies on population drawn from industries such as mining, textiles, and insulation, the report said.
It was found that the number of deaths reported in these studies ranged from one to 36. In addition it was found that in all of the studies in which more than 10 deaths from cancer of the larynx were reported, the relative risk for cancer was greater than one for exposed persons, on comparisons to those without exposure to asbestos.
The control studies revealed only one with a relative risk for cancer below one. Still the overall risk was very similar to that found in the cohort studies: Exposed persons had a relative risk of 1.43 for cancer, compared to non-exposed subjects. The 95% confidence interval ranged from 1.15 to 1.78.
Compiling 10 studies considered to have the best information on exposure as well as combining relative risk in those analyses revealed that the risk of cancer was at 1.21 for exposed subjects, but still significant. The 95% confidence interval ranged from 1.04 to 1.40.
After adjusting for risk factors like tobacco and alcohol use, the relative risk of cancer for an exposed person became 1.18, with a 95% confidence interval from 1.01 to 1.37.
The IOM stated the following biologically plausible reasons for the link between asbestos and laryngeal cancer:
1. The larynx lies anatomically in the direct path of inhaled asbestos fibers.
2. Squamous-cell carcinomas of the lung and larynx are both clinically and histologically similar.
3. Inflammation or damage to the vocal folds could disrupt the smooth flow of inhaled and exhaled air and allow asbestos fibers to build up in the larynx.
4. Cancers of both lung and larynx arise from the respiratory epithelium.
5. Tobacco is the chief risk factor for cancer at both sites.
The report however reports that there was insufficient evidence that asbestos fibers accumulate and persist in the larynx as well as a lack of experimental animal studies to support this