Mesothelioma pleural

ASBESTOS, in various forms, is a well-known risk factor for certain diseases. Pleural cancer is related to occupational exposure [1,2] (asbestos or fibers of industrial origin) and environmental exposure (e.g., natural fibers in the soil of a region, local industries that use certain materials, asbestos in building materials). [3-5] Persons who live with an occupationally exposed member of the household can also experience exposure. [6]

Within the framework of a study on the relationship between respiratory cancer and occupational exposure in the nickel industry, we collected data on all respiratory cancer cases, including cancer of the pleura, that were diagnosed during a 10-y period (i.e., 1978-1987). In an incidence study and in a case-control study within a cohort of nickel-exposed workers, [7] nickel exposure was excluded in New Caledonia as a risk-factor of respiratory cancer, including, as expected, cancer of the pleura.

The authors considered the possible pathological role of natural asbestos fibers in the soil, especially in the nickel mines, [8,9] to be of sufficient interest to warrant study.

Materials and methods

New Caledonia is a large island in the Southern Pacific region. Of the approximately 145 000 inhabitants, 40% are Melanesian and 40% are European.

All pleural cancer cases that were diagnosed during the preceding 10-y period were reviewed in France by a Certification Committee that was composed of pneumology experts. The cases were then submitted for certification to the French National Committee of Mesothelioma. Twelve cases were certified as primitive pleural cancers, of which 9 were mesothelioma cases. The remaining 3 were probable cases, but clinico-pathological evidence was insufficient. The characteristics of the cases are shown in Table 1.

Residence and occupational history information for the 12 cases was reconstructed during an interview with a family member. Information included details on [TABULAR DATA OMITTED]

all places of residence (name of the town or village, years of arrival and departure) and a description of all employment activities (i.e., type of work and dates of employment that were related to occupational exposure, if any).

The incidence of pleural cancer in New Caledonia was compared with five reference cancer registers that were representative of (a) different levels of industrialization; (b) the Anglo-Saxon and French lifestyles; and (c) various regions of the world, including the Pacific. Standardized Incidence Ratios (SIRs) were calculated by indirect standardization and were based on the age structure of the population. The observed number of cases was compared with the number expected (Poisson).

Results

The comparisons between cases in New Calendonia and the 5 reference registers are presented in Table 2. In all instances, the observed number of cases of pleural cancer in New Calendonia was higher than expected. The differences were statistically significant for the population as a whole and also for Melanesians.

The excess of pleural cancer cases was low compared with the results of other observations in nonoccupationally exposed populations, [10] and it could be related to an environmental or occupational factor. Identification of a possible cause for this excess in New Caledonia was investigated, and residential and occupational histories of the 12 cases were examined.

The interviews revealed that all 12 patients had lived at least part of their lives in rural areas (i.e., the bush). Other characteristics that were related to residence were extremely variable (Fig. 1). Some patients had always resided in the bush in the same region (i.e., Hienghene region, case no. 5; Kouaoua region, case no. 9; Moindou region, case no. 11; Bourail region, case no. 7). With the exception of a stay at Paita, case no. 2 had always lived on Lifou island. Case no. 12 resided in the bush for the shortest period of time (i.e., 2 y in the village of Yate).

Only two cases lived primarily in Noumea, which is the largest city (Fig. 1). One-half of the total population of New Caledonia lives in Noumea. The two cases were 58 and 61 y of age at the time of diagnosis. However, the youngest cases (31, 35, and 40 y of age at diagnosis) lived primarily in the central region between Poya and Canala.

Occupational histories varied. Three patients worked in the nickel industry: case no. 4 was an engine driver at a mine for 6 y, case no. 10 was a bargeman for 9 y, and case no. 12 was a clerk in a mine for 1 y. Other cases had work connections with mines, either personally (e.g., transportation of ore by truck) or through their families (e.g., father, brother, husband). Only 3 cases (nos. 2, 3, and 5) did not mention contact with mining.

The 3 women who had mesothelioma (cases no. 7, 8 and 9) were Melanesians, and except for case no. 7 who had lived in the small town of Bourail for 6 y, they had always lived in a tribe (traditional residence). These 3 women maintained traditional occupations, and case no. 7 had been a cook while she lived in Bourail. Members of their families (father, brother, husband) had been nickel mine workers, but typically for periods that did not exceed 18 mo. Two of these 3 women were 31 and 35 y of age at the time of diagnosis, whereas the

[TABULAR DATA OMITTED]

youngest men were 40 and 50 y of age at the time of diagnosis.

Discussion

The data present the usual limitation: a lack of precision related to the retrospective mode of collecting.

Thirteen suspected cases of pleural cancer (8 men, 3 of whom were Melanesians; 5 women, 4 of whom were Melanesians) were eliminated from the study by the National Committee of Mesothelioma and/or by the Certification Committee because there was incomplete histological information or insufficient proof. The diagnosis of mesothelioma was possible, but there was insufficient clinicopathological evidence, and the experts were unable to make an alternative diagnosis. Therefore, the number of observed cases may have been understated, and the real over-incidence may have been slightly higher than that observed.

We did not find a risk of pleural cancer in the nickel workers in New Caledonia. The comparison of New Caledonia with more developed regions (e.g., New York State, which presented an excess of pleural mesothelioma for men and women compared with other states), showed that other industries that are usually at risk for mesothelioma (e.g., naval construction and repair, insulation, manufacture of asbestos-based products) were not implicated.

An environmental risk is plausible. The geographical distribution of the pulmonary cancer cases that were collected during the first 4 y of the study (1978-1981) indicates a relationship between these cancers and zones of residence. [11] Environment and lifestyle could account for this relationship. However, the risk of pleural cancers in New Caledonia is between 2 and 5 times higher than in the regions included by the reference registers (Table 2). This is much lower than the risks observed in other parts of the world (e.g., more than 1 000 times in a region of Turkey [10]).

A qualitative examination of case residence histories did not afford the establishment of a relationship with a particular area of the country, even with the region on the east coast north of Touho, which is the richest region in natural fibers (Fig. 1). Nor was there a relationship with proximity of nickel mining sites, the dust from which could contain natural fibers in very limited quantities. However, the small excess of risk could be attributed to low exposure to a yet-unidentified agent. [12-15] Some authors suggest that when occupationally unexposed cases are younger (in this study two women were 31 and 35 y of age), the cause might be environmental. [16-18]

The preliminary result must be confirmed, and it would be of interest to examine the presence and type of fibers in the atmosphere. [19]

References

[1] McDonald JC, McDonald AD, Sebastien P, Moy K. Health of vermiculite miners exposed to trace amounts of fibrous tremolite. Br J Ind Med 1988; 45:630-34.

[2] Hirsch A, Bignon J. Asbestos- and fiber-related tumors of the pleura. The pleura in health and disease. In: Chretien J, Bignon J, Hirsch A, eds. Lung biology in health and disease. New York: M Dekker, 1985; 507-20.

[3] Baris Yl, Bilir N, Artvinli M, Sahin AA, Kalyoncu F, Sebastien P. An epidemiological study in an Anatolian village environmentally exposed to tremolite asbestos. Br J Ind Med 1988; 45:838-40.

[4] Cooper WC, Murchio J, Popendorf W, Wenk HR. Chrysotile asbestos in a California recreational area. Science 1979; 206:685-88.

[5] Rohl AN, Langer AM, Selikoff IJ. Environmental asbestos pollution related to use of quarried serpentine rock. Science 1977; 196:1319-22.

[6] Vianna NJ, Polan AK. Nonoccupational exposure to asbestos and malignant mesothelioma in females. Lancet 1978; 20:1061-63.