Occupational asbestos exposure, smoking, and laryngeal carcinoma

Intensity-modulated radiation therapy reduces the dose to normal tissue in T2N0M0 squamous cell carcinoma of the glottic larynx

The purpose of this paper was to compare intensity-modulated radiation therapy (IMRT) and conventional planning for T2N0M0 squamous cell carcinoma (SQCC) of the glottic larynx. Three patients with T2N0M0 SQCC are presented who were treated with IMRT. Conventional plans were also generated for comparison purposes. Isodose distributions and dose-volume histograms (DVHs) were generated for all the plans to evaluate the fitness of the plan as well as the differential benefit of IMRT vs. conventional treatment. The isodose distributions that were obtained by the IMRT plan are much more conformal to the planning target volume (PTV) and clearly show that less healthy tissue is subjected to a high-dose level, thus reducing toxicity. IMRT offers better comformality without compromising the PTV coverage and delivers less dose to normal tissues as compared to conventional radiation therapy in T2N0M0 SQCC of the glottic larynx. With an increase in conformality, it is expected to have an increase in the therapeutic ratio.

Aerodigestive and gastrointestinal tract cancers and exposure to crocidolite (blue asbestos): incidence and mortality among former crocidolite workers

The objective of this article was to assess the association between the incidence and mortality from aerodigestive cancers and exposure to crocidolite (blue asbestos). Our study is a cohort study of former workers of the now-defunct crocidolite mining and milling operation at Wittenoom, Western Australia, who have been followed up since 1979 and on whom asbestos exposure and smoking information was known. Standardised mortality and incidence rates were used to compare former workers with the Western Australian male population. Cases were matched with up to 10 randomly assigned controls, and conditional logistic regression was used to examine the relationship between asbestos exposure, smoking status and cancer incidence. There were 129 incident cases from all cancers of interest and 57 deaths. Former workers had a significantly higher risk of mortality from upper aerodigestive cancers than the Western Australian male population. The incidence of upper and lower aerodigestive cancers was higher in the Wittenoom cohort but not significantly so. Cumulative exposure to asbestos did not appear to be associated with the incidence of stomach cancer, colorectal cancer or upper aerodigestive cancers. Smoking status was strongly associated with the incidence of upper aerodigestive cancers, with current smokers experiencing the greatest risk. Our study with longer and more complete follow-up, smoking information and a stronger study design does not show an association between cumulative asbestos exposure and stomach cancer or other gastrointestinal cancers. The excess mortality from upper aerodigestive cancers seen in this cohort of former asbestos workers compared to the Western Australian male population does not appear to be associated with exposure to crocidolite.

Does asbestos cause laryngeal cancer?

Asbestos is a known carcinogen. Its role in the aetiology of laryngeal cancer has been investigated and debated for the last three decades. Here, we consider much of the published evidence from post-mortem studies, cross-sectional, case-control and cohort studies. We feel that the weight of evidence does not support a causal association for asbestos with laryngeal cancer. The 'positive studies' raise important questions regarding an association; the opportunity may present itself to answer some of these as the incidence of asbestos-related malignancy is increasing in the UK and Europe.

Tobacco, alcohol, asbestos, and occupational risk factors for laryngeal cancer

Data from a hospital-based case-control study between 1985-1990 were used to examine the effects of tobacco, alcohol, asbestos, and other occupational exposures on laryngeal cancer risk in 194 white men with primary cancer of the larynx and 184 age-matched control subjects. A dose-dependent effect for current cigarette smoking was observed, with higher relative risks (RR) for supraglottic cancer (RR, 21.6 to 68) than for cancer of the glottis (RR, 5.5 to 20.7). Elevated RR for ex-smokers (RR, 4.8) and pipe and cigar smokers (RR, 4.3) did not vary by subsite. The effects of alcohol also showed dose-dependent effects, with higher RR for cancer of the supraglottis than glottis for heavy drinkers (207 ml or more/daily; RR, 9.6 versus 2.5) and binge drinkers (RR, 28.4 versus 8.3). A slightly elevated but not significant association was seen for asbestos exposure and glottic cancer (RR, 1.3). The RR did not increase linearly with the number of years employed in asbestos-related occupations. No relationship was observed between asbestos and cancer of the supraglottis. When examining the data for a synergistic effect of cigarette smoking and asbestos exposure, no excess risk was found. A significantly elevated risk was found for men exposed to diesel fumes (RR, 5.2). Elevated but not significant RR were seen for men chronically exposed to rubber (RR, 6.4) and wood dust or employed as construction laborers, auto mechanics, and other jobs. A significant inverse trend with body mass was observed for cancer of the supraglottis.

Laryngeal cancer and occupational exposure to asbestos

The risk of laryngeal cancer associated with occupational exposure to asbestos was evaluated by a review of published reports. In only two of 13 cohort studies was the standardized mortality ratio (SMR) significantly increased. Smoking (a risk factor for laryngeal cancer) may have been more prevalent among asbestos workers than among the comparison populations. This was not taken into account in any of the studies, and may have caused the SMRs to be overestimated. Two of eight case-control studies reported large odds ratios (greater than or equal to 13) for laryngeal cancer. Subsequent case-control studies did not confirm this higher risk; the odds ratios in these studies were 0.3 to 1.9. The conclusion of the review, based on data from 13 cohort and 8 case-control studies, is that neither case-control nor cohort studies have established an increased risk of laryngeal cancer for asbestos workers.

Asbestos-related malignancy

Asbestos-associated malignancies have received significant attention in the lay and medical literature because of the increasing frequency of two asbestos-associated tumors, lung carcinoma and mesothelioma; the wide distribution of asbestos; its status as a prototype environmental carcinogen; and the many recent legal compensation proceedings, for which medical testimony has been required. The understanding of asbestos-associated carcinogenesis has increased through study of animal models, human epidemiology, and, recently, the application of modern molecular biological techniques. However, the detailed mechanisms of carcinogenesis remain unknown. A wide variety of malignancies have been associated with asbestos, although the strongest evidence for a causal association is confined to lung cancer and mesothelioma. Epidemiological studies have provided evidence that both the type of asbestos fiber and the industry in which the exposure occurs may affect the rates of asbestos-associated cancers. It has been shown that asbestos exerts a carcinogenic effect independent of exposure to cigarette smoking that, for lung cancers, is synergistically enhanced by smoking. Other questions remain controversial, such as whether pulmonary fibrosis necessarily precedes asbestos-associated lung cancer and whether some threshold level of exposure to asbestos (including low-dose exposures that may occur in asbestos-associated public buildings) may be safe. Mesothelioma, the most closely asbestos-associated malignancy, has a dismal natural history and has been highly resistant to therapy. However, investigational multi-modality therapy may offer benefit to some patients. A description of the processes through which compensation claims for asbestos-associated malignancies are evaluated illustrates for physicians the legal system's approach to possible injury from toxic substances. The differences between scientific and legal reasoning about the causes of diseases with long latency, especially when they are imputed to toxic exposures are substantial, and may impede the application of toxicological evidence to legal disputes.

Asbestos fibers in human pulmonary and extrapulmonary tissues

The association between asbestos fibers in human lung tissues and those in other extrapulmonary organs was studied by analysing three autopsied cases, one of whom had a high pulmonary asbestos burden, one an intermediate burden, and one a low burden. The amount, types and sizes of asbestos fibers in the tissues of lung, liver, spleen, pancreas, kidney, and gastrointestinal tract were identified and measured by transmission electron microscopy equipped with an energy dispersive X-ray analyser. The following results were obtained: 1) The concentrations of asbestos fibers in extrapulmonary organs tended to increase with that in lung tissues. 2) The types of fibers identified in lungs were approximately consistent with those in other organs. 3) A relatively large range of fiber length was observed in both lungs and other organs. The findings extend and support previous light microscopic studies comparing asbestos bodies in various organs, and may imply that persons with high levels of asbestos in their lungs are also likely to have the same types and high levels of asbestos in their other tissues.

Asbestos-related malignancy

Due to the known association with asbestos exposure, malignant mesothelioma has assumed an importance out of proportion to its incidence in the American population (2.2 per million). Patients present with chest pain, shortness of breath, or both. The initial chest X-ray generally reveals a large unilateral pleural effusion. A large piece of tissue obtained via open biopsy is usually required for histologic diagnosis. Investigational approaches include multiple needle biopsies obtained for electron microscopy, as well as for immunoperoxidase staining for keratin and CEA. The tumor characteristically remains localized until late in its course. The treatment of mesothelioma remains unsatisfactory. However, anecdotes report long-term disease-free survival after intensive treatment. Palliation with a response rate of up to 30% to various chemotherapeutic regimens has been reported by a number of investigators.

Occupational causes of laryngeal cancer

In a case-control study of all new cases of laryngeal cancer in Denmark from 1980 to 1982, 326 cases and 1134 community selected controls participated. Questionnaires were used to obtain information on education, occupation, and number of occupational exposures as well as smoking and drinking habits. High risk ratios for laryngeal cancer were found for semiskilled and unskilled workers, workers exposed to dust, out of doors workers, drivers, and people working in the cement industries and port services. The study hypothesis was that exposure to chromium or nickel increases the incidence rate of laryngeal cancer. No support for this was found concerning chromium, but exposure to nickel had a statistically significant risk ratio of 1.7.

Occupational risk for laryngeal cancer

In a case-control analysis, we studied the effects of type of employment on laryngeal cancer risk using the interview data from the Third National Cancer Survey. Effects were measured relative to the risk for those employed in a group of arbitrarily defined industries and occupations with low risk. We excluded females and controlled for age, tobacco use, alcohol use, and race in the analysis. We found ratio estimates above 3.0 for workers in the railroad industry and the lumber industry; and for sheetmetal workers, grinding wheel operators, and automobile mechanics.

Laryngeal cancer: an explanation for the apparent occupational association

The apparent association of laryngeal cancer with asbestos and possibly other occupational exposures can be accounted for by the hypothesis that chronic vocal abuse peculiar to certain working conditions will act as a promoting factor for active carcinogens found mainly in tobacco smoke.

Asbestos fibers in laryngeal tissues. Findings in two patients with asbestosis associated with laryngeal tumors

Significant concentrations of asbestos fibers have been found in samples of laryngeal tissue from two patients with past exposure to asbestos and associated asbestosis. In one case, there was a polyp on a vocal cord and in the other one a laryngeal carcinoma. These findings could provide an indication of a local carcinogenic effect of asbestos fibers in laryngeal tissue.

Tritiated thymidine as a broad spectrum initiator in transplacental two-stage carcinogenesis, with phorbol as promoter

A single subcutaneous injection of 200 mu Ci [3H] thymidine into pregnant BALD/c mice, followed by intraperitoneal injections of phorbol, twice weekly for 25 weeks, in the offspring, resulted in higher tumour development in the lungs and livers of male and, to a lesser extent, of female offspring, than in their untreated littermates. The difference in overall tumour incidence was statistically significant, but the increases of the individual tumour types were only of borderline significance. Slight carcinogenic activity of [3H]thymidine alone was observed in the mothers, and in the offspring, without phorbol treatment. The results suggest the possibility of using [3H]thymidine as a broad spectrum initiator for transplacental two-stage carcinogenicity studies to determine the organ specificity of different promoting agents.