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Clinicopathologic and survival characteristics of malignant pleural mesothelioma registered in hospital cancer registry.

Background Malignant pleural mesothelioma (MPM) is a rare but fatal thoracic tumor, which in the majority of patients is caused by prolonged exposure to asbestos fibers. We aimed at presenting clinicopathological and treatment outcomes of 60 patients of MPM registered in our hospital cancer registry. Materials and Methods Demographic characteristics of patients, exposure to asbestos, smoking habit, their clinicopathologic characteristics and survival analysis were described. Results Sixty patients had MPM. Forty patients (66.7%) were men. The mean age of patients was 55.8±11 years. Chest pain and dyspnea were the most prevalent symptoms (31.7%, and 30%, respectively). Thirty-six (61.7%) patients reported asbestos exposure. The median survival and Progression free survival (PFS) were 10.5 months (0.95CI=9.22-11.78) and 7.57 months (0.95CI=5.68-9.45), respectively. In multivariate analysis, exposure to asbestos and epithelioid subtype significantly extended the survival time. Bilateral involvement, high blood level of LDH and platelet count ≥400,000 significantly shortened the overall survival. Conclusion MPM is still an important health problem in Iran. Given the aforementioned results, developing a national program to eliminate asbestos-related diseases according to the world health organization (WHO) recommendation is necessary.


INTRODUCTION
Malignant pleural mesothelioma (MPM) is a rare but fatal thoracic malignancy (1,2). The incidence of MPM in the industrial world is increasing (3)(4)(5). The life expectancy of MPM is low and its median overall survival is 9 to 12 months (6). It is caused by prolonged occupational or environmental exposure to mineral fibers including asbestos and/or Erionite (7). The time period between the first exposure to asbestos fibers and overt disease is between 30-40 years (8,9).
Asbestos is still used by brake and clutch manufacturers in Iran (10,11). About 55,000 tons of asbestos is imported to Iran annually most of which is used in cement industries (12). Also, about 2,000 tons of asbestos is used in production of friction materials in the country TANAFFOS annually and about 3,000 workers are exposed to asbestos fibers in brake and clutch production industries (13).
In 2010, a hospital-based cancer registry was established in Masih Daneshvari Hospital to collect thoracic cancer data to be used for treatment monitoring and survival assessments. This is the first article using the registry data. In this study, we aimed at presenting clinicoepidemiological and treatment specifications of MPM cases whose data were registered. Reporting the survival rate and discussing its determinants such as sex, chemotherapy regimen, chief complaint, exposure to asbestos and histologic subtype was our other objective. Their survival time and its predictors were described using Kaplan-Meier method and Cox proportional hazard.

MATERIALS AND METHODS
All cases of thoracic cancers are reported to the cancer registry unit by the thoracic surgery, oncology and outpatient wards. A registry staff member, who is also a physician, interviews patients and fills out the data sheets.
The physician systematically monitors the patient status. In case the patient dies, the exact time of death is reported by the first-degree relatives. Based on the history of exposure to asbestos, four categories were defined: (i) Occupational exposure, (ii) Environmental exposure, (iii) No exposure, (iv) Unknown. Also, history of asbestos exposure was reported as (i) Yes or (ii) No.
History of smoking was categorized as smoker (currently smoking up to the time of diagnosis or exsmoker) and non-smoker (those who had never smoked).
According to the pathology results, patients' diagnoses were divided into four groups of (i) Epithelioid, (ii) Sarcomatoid, (iii) Mixed and (iv) Unspecified cell type. The staging was determined according to the AJCC seventh edition (14). Multimodality was defined as surgery (extra pleural pneumonectomy) + chemotherapy ± radiotherapy (15,16). Bilateral involvement was found in 11 cases (18.33%). All the demographic and clinicopathological characteristics are presented in Table 1.  (Figures 1 and 2).
In univariate analysis, none of the differences were statistically significant except for the variable platelet count. The median OS in patients with platelet count less than 400,000 was significantly more than that in subjects with platelet count ≥400,000 ( (Table 2).    found. Based on our study, 60 cases were diagnosed within three years and we can speculate that this difference indicates an increasing trend in the incidence of disease or improvement of diagnosis.
The prevalent symptoms were chest pain and dyspnea, similar to other studies (19). The most common histology subtype was epithelial, which is in accordance with other researches (15,20). Only 6 (10%) patients were eligible to undergo multimodality therapy and lived longer (22.7 months vs. 10.3 months). This is consistent with the findings of other researches (16).
Asbestos is still used in different industries in Iran (8).
Exposure to asbestos significantly extended the survival time. It could be due to clear history of past exposure and early diagnosis resulting in early treatment (21). The relationship between exposure to asbestos and developing mesothelioma has been documented earlier (22). About 61.7% of our patients reported exposure to asbestos, and only 32.43% of them were occupationally exposed. It means that source of exposure is not limited to work environments. Different studies report different history of asbestos exposure among cases of MPM. This could be due to different techniques used to assess exposure. Some investigators use lung tissue biopsy to detect asbestos fibers and some others perform patient interviews (7). The other reason relies on the fact that a substantial portion of exposures are non-occupational such as exposure to asbestos released from car brakes and clutches (13,23), exposure from living near industries where asbestos is used for manufacturing products, or even incidental exposure as occurred in two female cases who were contaminated by asbestos from their husbands' clothing (19). Males outnumbered females (7,24), which could be due to higher occupational exposure among men. More than two-thirds of the cases were between 51 and 70 years of age, which is consistent with other studies (7,15). The median overall survival of the patients who underwent therapy was 10.5 months (0.95CI, 9.22-11.78) (15,17,25).
Those with WBC count less than 10,000, non-smokers, subjects with left lung involvement (17) In our study, approximately 60% of patients had a history of asbestos exposure. We speculate that environment is potentially an important source of exposure to asbestos; possibly due to asbestos released by car brakes, clutch and manufacturing companies. Given the aforementioned findings, developing a national program to eliminate asbestos exposure and consequently asbestos-related diseases according to the WHO recommendation seems necessary (26).