Occupational and environmental causes of bronchogenic carcinoma

Theoretical approach to the hit probability of lung-cancer-sensitive epithelial cells by mineral fibers with various aspect ratios

BACKGROUND

  Inhalation of fibers may lead to the damage and, as a further consequence, to the malignant transformation of specific (most of all non-ciliated) cells of the bronchial and bronchiolar airway epithelium. In order to accurately estimate the cancer risk induced by inhaled fibers, hit probabilities of non-ciliated (secretory) cells by mineral fibers (asbestos and chrysotile) were computed.

METHODS

  Besides the use of a stochastic lung geometry and a particle transport/deposition model being based upon the random-walk algorithm, histological data of cell distributions in the human lungs were applied for the theoretical calculations. Diameters of computer-generated fibers ranged from 0.1 µm to 10 µm, whilst two values (3 and 100) were selected for the aspect ratios (ratios of fiber length to fiber diameter), thereby simulating the behavior of short and very long fibrous particles.

RESULTS

  According to the modeling results, the highest regional hit probabilities (up to 10%) are available for fibers with a diameter of 1.0 µm, whereby cells of the bronchiolar compartment represent a preferential target of these particles. For fibers with a diameter of 0.1 µm, bronchiolar hit probabilities reach 2-3%, whereas fibers with a diameter of 10 µm penetrate to the peripheral lung parts with only low amounts (<0.1%). A change of the inhalation conditions from sitting to light-work breathing enhances the extrathoracic and bronchial filtering of large particles (diameter ≥1 µm), whilst penetration of small particles towards distal lung airways is subject to a reinforcement. Further refinement of hit probabilities by considering single airway generations results in the circumstance that fibers with diameters ≤1.0 µm preferably collide with cancer-sensitive cells of airway generations 12-15. In contrast, fibers with a diameter of 10 µm mainly represent a hazard for cancer-sensitive cells being located in the uppermost airways. A change of breathing conditions both supports the effect of short fibers and enhances the filtering of long ones.

CONCLUSION

  Based upon the results of this contribution it can be concluded that highest cancer risk is generated by the inhalation of mineral fibers with diameters ≤1.0 µm, whereby fiber length has to be classified as a parameter with lower importance.

Pulmonary endpoints (lung carcinomas and asbestosis) following inhalation exposure to asbestos

Lung carcinomas and pulmonary fibrosis (asbestosis) occur in asbestos workers. Understanding the pathogenesis of these diseases is complicated because of potential confounding factors, such as smoking, which is not a risk factor in mesothelioma. The modes of action (MOA) of various types of asbestos in the development of lung cancers, asbestosis, and mesotheliomas appear to be different. Moreover, asbestos fibers may act differentially at various stages of these diseases, and have different potencies as compared to other naturally occurring and synthetic fibers. This literature review describes patterns of deposition and retention of various types of asbestos and other fibers after inhalation, methods of translocation within the lung, and dissolution of various fiber types in lung compartments and cells in vitro. Comprehensive dose-response studies at fiber concentrations inhaled by humans as well as bivariate size distributions (lengths and widths), types, and sources of fibers are rarely defined in published studies and are needed. Species-specific responses may occur. Mechanistic studies have some of these limitations, but have suggested that changes in gene expression (either fiber-catalyzed directly or by cell elaboration of oxidants), epigenetic changes, and receptor-mediated or other intracellular signaling cascades may play roles in various stages of the development of lung cancers or asbestosis.

Pemetrexed as first-line therapy for non-squamous non-small cell lung cancer

Pemetrexed is a new cytotoxic agent that is a standard of care for the second-line treatment of non-small cell lung cancer (NSCLC) and in combination with cisplatin in treatment of malignat pleural mesothelioma. It has been studied in numerous phase II and III trials in combination with different drugs or as single agent. Recently, pemetrexed has been approved in combination with cisplatin for the first-line treatment of patients with locally advanced or metastatic NSCLC other than squamous cell histology. The toxicity is acceptable and similar to that of other NSCLC regimens. The postinduction maintenance therapy with pemetrexed is being evaluated in a phase III, double-blind, placebo-controlled study.

Wood dust exposure and the association with lung cancer risk

BACKGROUND

Wood dust was designated as a human carcinogen based on increased sinus and nasal cancer rates among exposed workers. However, data on an association with lung cancer have been inconclusive.

METHODS

Self-reported wood dust exposure was compared between 1,368 lung cancer patients and 1,192 cancer-free adults, in a lung cancer case-control study. Epidemiological information was collected through a detailed personal interview.

RESULTS

Using several definitions of wood dust exposure we consistently observed statistically significant elevated adjusted risk estimates; for example, the adjusted odds ratio (OR) for combined wood dust related occupations and industries was 3.15 (95% confidence intervals (CI) 1.45-6.86) and for an overall summary exposure measure it was 1.60 (95% CI 1.19-2.14). The association was maintained when stratified by histopathological type. Among those exposed to cigarette smoke and wood dust, 21% of the cases were attributable to biologic interaction.

CONCLUSIONS

Wood dust exposure is a potential risk factor for lung cancer.

Lung cancer

Lung cancer is the leading cause of cancer-related mortality. Since tobacco smoking is the cause in vast majority of cases, the incidence of lung cancer is expected to rise in those countries with high or rising incidence of tobacco smoking. Even though populations at risk of developing lung cancer are easily identified, mass screening for lung cancer is not supported by currently available evidence. In the case of non-small cell lung cancer, a cure may be possible with surgical resection followed by post-operative chemotherapy in those diagnosed at an early stage. A small minority of patients who present with locally advanced disease may also benefit from pre-operative chemotherapy and/or radiation therapy to down stage the tumor to render it potentially operable. In a vast majority of patients, however, lung cancer presents at an advanced stage and a cure is not possible with currently available therapeutic strategies. Similarly, small cell lung cancer confined to one hemi-thorax may be curable with a combination of chemotherapy and thoracic irradiation followed by prophylactic cranial irradiation, if complete remission is achieved at the primary site. Small cell lung cancer that is spread beyond the confines of one hemi-thorax is, however, considered incurable. In this era of molecular targeted therapies, new agents are constantly undergoing pre-clinical and clinical testing with the aim of targeting the molecular pathways thought be involved in etiology and pathogenesis of lung cancer.

Association between the Risk for Lung Adenocarcinoma and a (−4) G-to-A Polymorphism in the XPA Gene

Polymorphisms of genes coding for DNA repair can affect lung cancer risk. A common single nucleotide (−4) G-to-A polymorphism was identified previously in the 5′ untranslated region of the XPA gene. In a case-control study in European Caucasians, the influence of this polymorphism on primary lung cancer risk overall and according to histologic subtypes was investigated. Four hundred sixty-three lung cancer cases (including 204 adenocarcinoma and 212 squamous cell carcinoma) and 460 tumor-free hospital controls were investigated using PCR amplification and melting point analysis of sequence-specific hybridization probes. Odds ratios (OR) were calculated by multiple logistic regression analysis adjusting for age, gender, smoking habits, and occupational exposure and showed a slightly enhanced risk for all lung cancer cases as well as for squamous cell carcinoma and adenocarcinoma cases. Gene-environment interactions were analyzed with respect to smoking and occupational exposure. A nearly 3-fold increased risk for adenocarcinoma associated with the XPA AA genotype was observed for occupationally exposed individuals (OR, 2.95; 95% confidence interval, 1.42-6.14) and for heavy smokers (OR, 2.52; 95% confidence interval, 1.17-5.42). No genotype-dependent increase in OR was found for nonexposed individuals or those smoking &lt;20 pack-years. The significant effect of the XPA polymorphism in heavy smokers and occupationally exposed individuals suggests an important gene-environment interaction for the XPA gene. The underlying mechanisms as to why AA homozygotes are predisposed to lung adenocarcinoma and which specific carcinogens are involved remains to be determined.

Respiratory impairment due to asbestos exposure in brake-lining workers

There is extensive evidence that exposure to asbestos causes pulmonary parenchymal fibrosis, pleural disease, and malignant neoplasm in asbestos-exposed workers. However, few data concerning brake-lining workers are available in the literature. In this study, we aimed to assess the long-term effects of chrysotile asbestos exposure on lung function and the risk of asbestos-related diseases in brake-lining workers. Seventy-four asbestos-exposed workers who processed brake-lining products and 12 unexposed office workers were offered pulmonary function tests (spirometry and transfer factor) in 1992 and 1999. In 1999, the mean duration of asbestos exposure was 10.00+/-4.07 and 11.02+/-4.81 years (7-31 years) in nonsmoking and smoking asbestos workers, respectively. Transfer factor (T(L), CO) and transfer coefficient (K(CO)) decline were significant in the 7-year follow-up in both smoking and nonsmoking asbestos workers. However, lung function indices of the control group, whom were all current smokers; were also found to be decreased, including FEF(75), T(L), CO and K(CO). We found minimal reticular changes in 10 asbestos workers who were all current smokers, they underwent high-resolution computed tomography scans of the chest and we found that they had peribronchial thickening resulting from smoking. As a conclusion, even in the absence of radiographic asbestosis, T(L), CO and K(CO) may decrease after a mean 10-year duration of exposure to asbestos in brake-lining workers and this is more noticeable with cigarette burden.