Lung Cancer

Lung cancer is the most common cancer worldwide. In 1985, it is estimated that worldwide 676,500 cases occurred in males and 219,300 cases in females, accounting for 11.8% of all new cancers, and this figure is increasing at a rate of about 0.5% per year (Parkin, Pisani and Ferlay 1993). About 60% of these cases occur in industrialized countries, in many of which lung cancer is the leading cancer cause of death among males. In both industrialized and developing countries, males have a higher incidence than females, the sex ratio ranging from two- to ten-fold. The international intergender variations in lung cancer incidence are largely explained by the variation in current and past smoking patterns.

A higher lung cancer risk has been consistently observed in urban compared to rural areas. In industrialized countries, a clear, inverse relationship is evident in males in lung cancer incidence and mortality by social class, while women show less clear and consistent patterns. Differences in social class in males principally reflect a different smoking pattern. In developing countries, however, there seems to be a higher risk in men from the upper social class than in other men: this pattern probably reflects the earlier adoption of Western habits by affluent groups in the population.

Incidence data from the United States National Cancer Institute’s SEER Program for the period 1980-86 indicate, similarly to previous years, that Black males have a higher incidence than White males, while incidence for females does not differ by race. These differences among ethnic groups in the United States can actually be attributed to socio-economic differences between Blacks and Whites (Baquet et al. 1991).

Lung cancer incidence increases almost linearly with age, when plotted in a log-log scale; only in the oldest age groups can a downward curve be observed. Lung cancer incidence and mortality have increased rapidly during this century, and continue to increase in most countries.

There are four principal histological types of lung cancer: squamous cell carcinoma, adenocarcinoma, large cell carcinoma and small cell carcinoma (SCLC). The first three are also referred to as non-small cell lung cancer (NSCLC). The proportions of each histological type change according to sex and age.

Squamous cell carcinoma is very strongly associated with smoking and represents the most common type of lung cancer in many populations. It arises most frequently in the proximal bronchi.

Adenocarcinoma is less strongly associated with smoking. This tumour is peripheral in origin and may present as a solitary peripheral nodule, a multifocal disease or a rapidly progressive pneumonic form, spreading from lobe to lobe.

Large cell carcinoma represents a smaller proportion of all lung cancers and has a similar behaviour as adenocarcinoma.

SCLC represents a small proportion (10 to 15%) of all lung cancers; it typically arises in the central endobronchial location and tends to develop early metastases.

The signs and symptoms of lung cancer depend on the location of the tumour, the spread and the effects of metastatic growth. Many patients present with an asymptomatic lesion discovered incidentally on x ray. Among NSCLC patients, fatigue, decreased activity, persistent cough, dyspnoea, decreased appetite and weight loss are common. Wheeze or stridor may also develop in advanced stages. Continuous growth may result in atelectasia, pneumonia and abscess formation. Clinical signs among SCLC patients are less pronounced than among those with NSCLC, and are usually related to the endobronchial location.

Lung cancer can metastasize to virtually any organ. The most common locations of metastatic lesions are pleura, lymph nodes, bone, brain, adrenals, pericardium and liver. At the moment of diagnosis, the majority of patients with lung cancer have metastases.

The prognosis varies with the stage of the disease. Overall five-year survival for lung cancer patients in Europe (in 1983-85) was between 7% and 9% (Berrino et al. 1995).

No population screening method is currently available for lung cancer.

Nasopharyngeal Cancer

Nasopharyngeal cancer is rare in most populations, but is frequent in both sexes in areas such as South-East Asia, Southern China and North Africa. Migrants from South China retain the high risk to a large extent, but second- and third-generation Chinese migrants to the United States have less than half the risk of first generation migrants.

Cancers of the nasopharynx are predominantly of squamous epithelial origin. According to WHO, these tumours are classified as: type 1, keratinizing squamous cell carcinoma; type 2, non-keratinizing carcinoma; and type 3, undifferentiated carcinoma, which is the most frequent histological type. Type 1 has an uncontrolled local growth, and metastatic spread is found in 60% of the patients. Types 2 and 3 have metastatic spread in 80 to 90% of the patients.

A mass in the neck is noticed in approximately 90% of nasopharyngeal carcinoma patients. Alterations in the hearing, serous otitis media, tinnitus, nasal obstruction, pain and symptoms related to the growth of the tumour into adjacent anatomical structures may be noticed.

The overall five-year survival for nasopharyngeal cancer patients in Europe between 1983 and 1985 was around 35%, varying according to the stage of the tumour and its location (Berrino et al. 1995).

Consumption of Chinese-style salted fish is a risk factor of nasopharyngeal cancer; the role of other nutritional factors and of viruses, in particular Epstein-Barr virus, although suspected, has not been confirmed. No occupational factors are known to cause nasopharyngeal cancer. No preventive measures are available at present (Higginson, Muir and Muñoz 1992).

Sinonasal Cancer

Neoplasms of the nose and nasal cavities are relatively rare. Together, cancer of the nose and nasal sinus—including maxillary, ethmoidal, sphenoid and frontal sinuses—account for less than 1% of all cancers. In most cases these tumours are classified as squamous carcinomas. In Western countries, cancers of the nose are more common than cancers of the nasal sinus (Higginson, Muir and Muñoz 1992).

They occur more frequently in men and among Black populations. The highest incidence is seen in Kuwait, Martinique and India. The peak of development of the disease occurs during the sixth decade of life. The major known cause of sinonasal cancer is exposure to wood dust, in particular from hardwood species. Tobacco smoking does not seem to be associated with this type of cancer.

Most tumours of the nasal cavity and para-nasal sinus are well differentiated and slow growing. Symptoms may include non-healing ulcer, bleeding, nasal obstruction and symptoms related to the growth into the oral cavity, orbit and pterygoid fossa. The disease is usually advanced at the time of diagnosis.

Overall five-year survival for nose and nasal sinus cancer patients in Europe between 1983 and 1985 was around 35%, varying according to the size of the lesion at diagnosis (Berrino et al. 1995).

Laryngeal Cancer

The highest incidence of laryngeal cancer is reported in Sao Paolo (Brazil), Navarra (Spain) and Varese (Italy). High mortality has also been reported in France, Uruguay, Hungary, Yugoslavia, Cuba, the Middle East and North Africa. Laryngeal cancer is predominantly a male cancer: an estimated 120,500 cases among males and 20,700 cases among females occurred in 1985 (Parkin, Pisani and Ferlay 1993). In general, incidence is higher among Black populations as compared to Whites, and in urban areas compared to rural.

Almost all cancers of the larynx are squamous carcinomas. The majority are located in the glottis, but they may also develop in the supraglottis or, rarely, in the subglottis.

Symptoms may not occur or be very subtle. Pain, a scratchy sensation, alteration of tolerance for hot or cold foods, a tendency to aspirate liquids, airway alteration, a slight change in the voice during several weeks and cervical adenopathy may be present, according to the location and stage of the lesion.

Most larynx cancers are visible with laryngeal inspection or endoscopy. Pre-neoplastic lesions can be identified in the larynx of smokers (Higginson, Muir and Muñoz 1992).

The overall five-year survival for laryngeal cancer patients in Europe between 1983 and 1985 was around 55% (Berrino et al. 1995).

Pleural Mesothelioma

Mesotheliomas may arise from the pleura, peritoneum and pericardium. Malignant mesothelioma represents the most important pleural tumour; it occurs mainly between the fifth and seventh decade of life.

Pleural mesothelioma was once a rare tumour and remains so in most female populations, while in men in industrialized countries it has increased by 5 to 10% per year during the last decades. In general, men are affected five times as much as women. Precise estimates of incidence and mortality are problematic because of difficulties in the histological diagnosis and changes in the International Classification of Diseases (ICD) (Higginson, Muir and Muñoz 1992). However, incidence rates seem to present very important local variations: they are very high in areas where asbestos mining is present (e.g., North West Cape Province of South Africa), in major naval dockyard cities, and in regions with environmental fibre contamination, such as certain areas of central Turkey.

Patients may be asymptomatic and have their disease diagnosed incidentally on chest radiographs, or they may have dyspnoea and chest pain.

Mesotheliomas tend to be invasive. The median survival is 4 to 18 months in various series.

Occupational Risk Factors of Respiratory Cancer

Apart from tobacco smoke, a causal association with respiratory cancer has been demonstrated according to the International Agency for Research on Cancer (IARC) for 13 agents or mixtures and nine exposure circumstances (see table 1). Furthermore, there are eight agents, mixtures or exposure circumstances which according to IARC are probably carcinogenic to one or more organs in the respiratory tract (table 2). All but azathioprine, an immunosuppressant drug, are primarily occupational exposures (IARC 1971-94).

Table 1. Established human respiratory carcinogens according to IARC

 Source: IARC, 1971-1994.

Table 2. Probable human respiratory carcinogens according to IARC

Source: IARC, 1971-1994.

Occupational groups demonstrating an increased risk of lung cancer following exposure to arsenic compounds include non-ferrous smeltery workers, fur handlers, manufacturers of sheep-dip compounds and vineyard workers (IARC 1987).

A large number of epidemiological studies have been carried out on the association between chromium (VI) compounds and the occurrence of lung and nasal cancer in the chromate, chromate pigment and chromium plating industries (IARC 1990a). The consistency of findings and the magnitude of the excesses have demonstrated the carcinogenic potential of chromium (VI) compounds.

Nickel refinery workers from many countries have shown substantial increased risks of lung and nasal cancers; other occupational groups exposed to nickel among which an increased risk of lung cancer has been detected include sulphide nickel ore miners and high nickel alloy manufacture workers (IARC 1990b).

Workers exposed to beryllium are at elevated risk of lung cancer (IARC 1994a). The most informative data are those derived from the US Beryllium Case Registry, in which cases of beryllium-related lung diseases were collected from different industries.

An increase in lung cancer occurrence has been found in cohorts of cadmium smelters and nickel-cadmium battery workers (IARC 1994b). Concurrent exposure to arsenic among smelters and to nickel among battery workers, cannot explain such an increase.

Asbestos is an important occupational carcinogen. Lung cancer and mesothelioma are the major asbestos-related neoplasms, but cancers at other sites, such as the gastro-intestinal tract, larynx and kidney, have been reported in asbestos workers. All forms of asbestos have been causally related to lung cancer and mesothelioma. In addition, talc-containing asbestiform fibres have been shown to be carcinogenic to the human lung (IARC 1987). A distinctive characteristic of asbestos-induced lung cancer is its synergistic relationship with cigarette smoking.

A number of studies among miners, quarry workers, foundry workers, ceramic workers, granite workers and stone cutters have shown that individuals diagnosed as having silicosis after exposure to dust containing crystalline silica have an increased risk of lung cancer (IARC 1987).

Polynuclear aromatic hydrocarbons (PAHs) are formed mainly as a result of pyrolytic processes, especially the incomplete combustion of organic materials. However, humans are exposed exclusively to mixtures of PAHs, such as soots, coal-tars and coal-tar pitches. Cohort studies of mortality among chimney-sweeps have shown an increased risk of lung cancer, which has been attributed to soot exposure. Several epidemiological studies have shown excesses of respiratory cancer among workers exposed to pitch fumes in aluminium production, calcium carbide production and roofing. In these industries, exposure to tar, and particularly coal tar, does also occur. Other industries in which an excess of respiratory cancer is due to exposure to coal-tar fumes are coal gasification and coke production (IARC 1987). An increased risk of respiratory (mainly lung) cancer was found in some, but not all the studies tried to analyse diesel engine exhaust exposure separately from other combustion products; the occupational groups which were studied include railroad workers, dockers, bus garage workers, bus company employees and professional lorry drivers (IARC 1989a). Other mixtures of PAHs that have been studied for their carcinogenicity to humans include carbon blacks, gasoline engine exhaust, mineral oils, shale oils, and bitumens. Shale oils and untreated and mildly treated mineral oils are carcinogenic to humans, whereas gasoline engine exhaust is possibly carcinogenic and highly refined mineral oils, bitumens and carbon blacks are not classifiable as to their carcinogenicity to humans (IARC 1987, 1989a). Although these mixtures do contain PAHs, a carcinogenic effect on the human lung has not been demonstrated for any of them, and the evidence of carcinogenicity for untreated and mildly treated mineral oils and for shale oils is based on increased risk of cancers from sites other than respiratory organs (mainly skin and scrotum) among exposed workers.

Bis(b-chloroethyl)sulphide, known as mustard gas, was widely used during the First World War, and the studies of soldiers exposed to mustard gas as well as of workers employed in its manufacture have revealed a subsequent development of lung and nasal cancer (IARC 1987).

Numerous epidemiological studies have demonstrated that workers exposed to chloromethyl methyl ether and/or bis(chloromethyl)-ether have an increased risk of lung cancer, primarily of SCLC (IARC 1987).

Workers exposed to acrylonitrile have been found to be at higher risk of lung cancer in some but not all studies which have been conducted among workers in textile fibre manufacture, acrylonitrile polymerization and the rubber industry (IARC 1987).

Excess occurrence has been reported for workers exposed to formaldehyde, including chemical workers, wood workers, and producers and users of formaldehyde (IARC 1987). The evidence is strongest for nasal and nasopharyngeal cancer: the occurrence of these cancers showed a dose-response gradient in more than one study, although the number of exposed cases was often small. Other neoplasms at possible increased risk are lung and brain cancer and leukaemia.

An increased risk of laryngeal cancer has been found in several studies of workers exposed to mists and vapours of sulphuric and other strong inorganic acids, such as workers in steel pickling operations, and in soap manufacture and petrochemical workers (IARC 1992). Lung cancer risk was also increased in some, but not all, of these studies. Furthermore, an excess of sinonasal cancer was found in a cohort of workers in isopropanol manufacture using the strong-acid process.

Woodworkers are at increased risk of nasal cancer, in particular adenocarcinoma (IARC 1987). The risk is confirmed for furniture and cabinet-makers; studies on workers in carpentry and joinery suggested a similar excess risk, but some studies produced negative results. Other wood industries, such as sawmills and pulp and paper manufacture, were not classifiable as to their carcinogenic risk. Although carcinogenicity of wood dust was not evaluated by IARC, it is plausible to consider that wood dust is responsible for at least part of the increased risk of nasal adenocarcinoma among woodworkers. Woodworkers do not seem to be at increased risk of cancer in other respiratory organs.

Nasal adenocarcinoma has been caused also by employment in boot and shoe manufacture and repair (IARC 1987). No clear evidence is available, on the other hand, that workers employed in the manufacture of leather products and in leather tanning and processing are at increased risk of respiratory cancer. It is not known at present whether the excess of nasal adenocarcinoma in the boot and shoe industry is due to leather dust or to other exposures. Carcinogenicity of leather dust has not been evaluated by IARC.

Lung cancer has been common among uranium miners, underground hematite miners and several other groups of metal miners (IARC 1988; BEIR IV Committee on the Biological Effects of Ionizing Radiation 1988). A common factor among each of these occupational groups is exposure to a-radiation emitted by inhaled radon particles. The main source of data on cancer following exposure to ionizing radiation is derived from the follow-up of atomic bomb survivors (Preston et al. 1986; Shimizu et al. 1987). The risk of lung cancer is elevated among the atomic bomb survivors as well as among people who have received radiation therapy (Smith and Doll 1982). No convincing evidence, however, is currently available on the existence of an elevated lung cancer risk among workers exposed to low-level ionizing radiation, such as those occurring in the nuclear industry (Beral et al. 1987; BEIR V, Committee on the Biological Effects of Ionizing Radiation 1990). Carcinogenicity of ionizing radiation has not been evaluated by IARC.

An elevated risk of lung cancer among painters was found in three large cohort studies and in eight small cohort and census-based studies, as well as eleven case-control studies from various countries. On the other hand, little evidence of an increase in lung cancer risk was found among workers involved in the manufacture of paint (IARC 1989b).

A number of other chemicals, mixtures, occupations and industries which have been evaluated by IARC to be carcinogenic to humans (IARC Group 1) do not have the lung as the primary target organ. Nonetheless, the possibility of an increased risk of lung cancer has been raised for some of these chemicals, such as vinyl chloride (IARC 1987), and occupations, such as spraying and application of insecticides (IARC 1991a), but the evidence is not consistent.

Furthermore, several agents which have the lung as one of the main targets, have been considered to be possible human carcinogens (IARC Group 2B), on the basis of carcinogenic activity in experimental animals and/or limited epidemiological evidence. They include inorganic lead compounds (IARC 1987), cobalt (IARC 1991b), man-made vitreous fibres (rockwool, slagwool and glasswool) (IARC 1988b), and welding fumes (IARC 1990c).

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