Pleural malignant mesothelioma in Tuscany, Italy (1970-1988): I. Anatomo-pathologic aspects

Malignant mesothelioma of the pleura: interobserver variability

AIMS

To assess the consistency of histopathological diagnosis of pleural malignant mesothelioma by estimating interobserver agreement between five pathologists.

METHODS

Eighty eight histological sets pertaining to original diagnoses of pleural malignant mesothelioma were reviewed separately by each pathologist. Diagnostic likelihood was graded as definite (A), probable (B), possible (C), improbable (D), and definitely not (E) malignant mesothelioma. The following indexes were estimated: observed proportion of agreement (Po), kappa statistics and proportion of agreement for "positive" (Ppos) and "negative" (Pneg) diagnoses.

RESULTS

Sixty cases (68.2%) were rated by at least three reviewers as A or B and by none of the others as D or E. Five (5.7%) were rated by at least two reviewers as D or E and by none of the others as A or B. Nine (10.2%) showed a serious disagreement, rated A or B and D or E. Agreement for sets obtained at necropsy/surgery (median kappa w = 0.57) was similar to that for endoscopic material (median kappa w = 0.54). Agreement was poor on material obtained by needle biopsy (median kappa w = 0.21). The median value of Ppos varied between 0.94 (necropsy/surgery) and 0.67 (needle biopsy) and that of Pneg between 0.78 (necropsy/surgery) and 0.34 (unspecified biopsy). Interobserver agreement on histological typing was good overall (median kappa = 0.59).

CONCLUSIONS

Of the original histological diagnoses, 70% were consistently reproduced through panel review. Most indexes of agreement between pathologists ranged from poor (needle biopsy) to moderate (necropsy/surgery). Agreement in confirming malignant mesothelioma was greater than that regarding exclusion of this diagnosis. Of the cases finally considered to have malignant mesothelioma, the reproducibility of histological typing was relatively satisfactory.

Continuing increase in mesothelioma mortality in Britain

Mesothelioma is closely related to exposure to asbestos, and mesothelioma mortality can be taken as an index of past exposure to asbestos in the population. We analysed mesothelioma mortality since 1968 to assess the current state of the mesothelioma epidemic, and to predict its future course. We found that rates of mesothelioma in men formed a clear pattern defined by age and date of birth. Rates rose steeply with age showing a very similar pattern in all five-year birth cohorts. By date of birth, rates increased from mid-1893 to mid-1948, and then fell. Relative to the 1943-48 cohort, the risk for the 1948-53 cohort is 0.79 and for the 1953-58 cohort 0.48. Despite these falls, if the age profile of rates for these cohorts follows the pattern of past cohorts, their predicted lifetime mesothelioma risks will be 1.3%, 1.0%, and 0.6%. Combining projections for all cohorts results in a peak of annual male mesothelioma deaths in about the year 2020 of between 2700 and 3300 deaths. If diagnostic trend is responsible for a 20% growth in recorded cases every 5 years--an extreme but arguable case--and if this trend has now ceased, the peak of annual male deaths will be reduced to 1300, reached around the year 2010. Analysis of occupations recorded on death certificates indicate that building workers, especially plumbers and gas fitters, carpenters and electricians are the largest high-risk group. These data indicate that mesothelioma deaths will continue to increase for at least 15 and more likely 25 years. For the worst affected cohorts--men born in the 1940s--mesothelioma may account for around 1% of all deaths. Asbestos exposure at work in construction and building maintenance will account for a large proportion of these deaths, and it is important that such workers should be aware of the risks and take appropriate precautions.

Pleural malignant mesothelioma in Tuscany, Italy (1970-1988): II. Identification of occupational exposure to asbestos

Following the finding of an unexpected cluster of mesotheliomas in textile workers, a surveillance system of malignant mesotheliomas was implemented in the region of Tuscany, Italy. This article reports on the investigation of 124 cases of mesothelioma diagnosed and reviewed by the Institutes of Morbid Anatomy and Histopathology at the Universities of Florence, Pisa, and Siena between 1970 and 1988. A complete occupational and asbestos exposure history was assessed through a semi-structured questionnaire directly administered to resident cases of Tuscany or, if deceased, to their closest living relatives, for a total of 100 interviews. The hypothesis of past occupational asbestos exposure was verified and documented. Seventy-two cases have been classified as occupationally exposed to asbestos; four were classified in the category of "possible domestic" exposure to asbestos. For two others, the role of other risk factors was stressed, and for 22 cases, either no asbestos exposure was found or the available data were not adequate to define it. The present study allowed identification of some unknown or scarcely known occupational asbestos exposures in the study area.