Lung fibre burden and risk of malignant mesothelioma in shipyard workers: a necropsy-based case-control study.

OBJECTIVES: In Italy, the highest pleural cancer mortality and incidence have been observed among Italian regions where the 2 largest Italian shipyards were (and are) located. The objective of this study was to assess the exposure-response relationship for mesothelioma among male workers employed in the Monfalcone, Italy, shipyard. METHODS: We conducted a necropsy-based case-control study. Cases (N = 102) were mesothelioma decedents and controls were those with lung cancer (N = 84). Complete job histories were available; the lung fibre content was measured using a scanning electron microscope with X-ray fluorescence, after sample preparation according to the European Respiratory Society guidelines. Odds ratios and 95% confidence intervals of mesothelioma by fibre type and lung fibre burden, as a categorical or continuous variable, were assessed by unconditional logistic regression, adjusted for age and time since exposure cessation. Analyses for the amphibole and chrysotile lung fibre burden were mutually adjusted. We calculated a cumulative exposure index by applying a job-exposure matrix to the job histories of study cases and assessed its correlation with the lung fibre burden. RESULTS: We found an odds ratio of 22.0 (confidence intervals 5.66-85.7) for the highest lung fibre burden category (mean 43.8 million total asbestos fibres per gram of dry tissue) compared with the reference (mean 0.48). Using log10-transformed lung fibre burden, we found that the odds ratio was 3.71 (confidence intervals 2.03-6.79) for a 10-fold lung fibre burden increase. Results for the amphibole lung fibre burden were similar. Odds ratios increased over chrysotile lung fibre burden categories (P-trend = 0.025), and the odds ratio for a 10-fold increase was 4.73 (confidence intervals 0.32-70.4). CONCLUSIONS: The cumulative exposure index was correlated with total and amphibole lung fibre burden, but not with chrysotile lung fibre burden. Mesothelioma risk was proportional to total, amphibole, and chrysotile lung fibre burden in shipyard workers.

Lung asbestos fiber burden analysis: effects of the counting rules for legal medicine evaluations.

OBJECTIVES: The work shows the effect of counting rules, such as analysis magnification and asbestos fiber dimension to be count (with length ≥5 µm or also asbestos fibers with length <5 µm) in the lung asbestos fiber burden analysis for legal medicine evaluations. METHODS: On the same lung tissue samples, two different analyses were carried out to count any asbestos fibers with length ≥1 µm and with length ≥5 µm. Results of the amphibole burden of the two analyses were compared by linear regression analysis on log10-transformed values. RESULTS: The analysis should be carried out at an appropriate magnification and on samples prepared in such a way as they allow the counting of very fine fibers. If the analysis is limited to the asbestos fibers with length ≥5 µm, there is a high risk of not detecting possible residual chrysotile fiber burden and thinner crocidolite asbestos fibers. CONCLUSIONS: On average we estimated that 1 amphibole fiber with length ≥5 µm corresponds to ∼8 amphibole fibers with length ≥1 µm in the lung. The values of the Helsinki criteria should be updated taking this into account.

Asbestos Lung Burden Does Not Predict Survival in Malignant Pleural Mesothelioma: A Necropsy-Based Study of 185 Cases.

INTRODUCTION: Malignant pleural mesothelioma is an asbestos-related disease with poor survival. The prognostic role of histologic subtype is well established. Some studies (without a biological hypothesis) suggested that higher asbestos lung burden is associated with reduced survival. METHODS: We selected subjects from two series of necropsies: residents in Brescia province (North-West Italy) and workers (or persons living with them) employed in the Monfalcone shipyards (North-East Italy). Asbestos fibers and asbestos bodies in lung samples were counted using a scanning electron and an optical microscope, respectively. Separately in the two series, we analyzed median survival time and fitted multivariable Cox regression models (adjusted for sex, period and age at diagnosis, and histopatholocical diagnosis) to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for three levels of asbestos fiber counts (reference: <1 million fibers/g of dry lung tissue). RESULTS: We analyzed 185 necropsies, 83 in Brescia and 102 in Monfalcone. Despite a much higher lung burden in Monfalcone patients, median survival was slightly shorter in Brescia (8.3 mo) than in Monfalcone (10.2 mo). In Brescia, medium (1.0-9.9) and high (10+) fiber burden HRs were 0.91 (95% CI: 0.54-1.53) and 1.23 (95% CI: 0.41-3.70), respectively. In Monfalcone, the corresponding HRs were 1.18 (95% CI: 0.59-2.35) and 1.63 (95% CI: 0.77-3.45), respectively. CONCLUSIONS: No relationship between asbestos lung burden and survival was found. Histologic subtype was the strongest prognostic determinant.

Accuracy of pleural biopsy for the diagnosis of histologic subtype of malignant pleural mesothelioma: Necropsy-based study of 134 cases.

BACKGROUND: Definition of histologic subtype of malignant pleural mesothelioma (MPM) is important for management of patients, because surgical treatment improves prognosis for patients with epithelioid but not biphasic or sarcomatoid MPM. In a series of necropsies performed in a hospital specialized for MPM diagnosis, we retrospectively investigated the accuracy of histologic diagnosis performed on pathologic specimens collected through pleural biopsies obtained at video-assisted thoracoscopic surgery (VATS) or surgery. METHODS: We reviewed histologic records of an unselected series of autopsies performed in patients with MPM employed in the Monfalcone shipyards (Northeast Italy) or living with shipyard workers from 1999 through 2017. Using necropsy results as a gold standard, we calculated sensitivity, specificity, and positive and negative predictive values of histology from VATS or surgery after combining nonepithelioid subtypes. RESULTS: We retrieved necropsy records for 134 patients: 62 (46.3%) with epithelioid, 51 (38.1%) with biphasic, and 21 (15.7%) with sarcomatoid MPM. We observed good sensitivity of VATS (0.94) and surgery (0.89) in diagnosing epithelioid MPM. Conversely, specificity was low (VATS: 0.46; surgery: 0.32). Therefore, positive predictive values were also low (VATS: 0.58; surgery: 0.60). Misclassification was particularly high for biphasic MPM (three-fourths of biphasic MPM at necropsy had been classified as epithelioid at VATS or surgery). CONCLUSIONS: We observed a substantial degree of misclassification between epithelioid and biphasic MPM for pleural biopsies performed during VATS. Our results suggest caution should be taken in using histologic subtype obtained from VATS in selecting patients with MPM for surgical treatment. We also observed substantial misclassification of biospecimens collected during MPM surgery.

[Pleural malignant mesotheliomas from environmental exposures to asbestos In Italy]. / Mesoteliomi maligni della pleura da esposizione ambientale ad amianto in Italia.

Pleural mesothelioma clusters from outdoor environmental exposure have been highlighted also in Italy and, on the basis of epidemiological surveillance coordinated by the Italian National Mesothelioma Register, their frequency has been estimated at about 4.5%. Epidemiological studies and evaluations of some regional mesothelioma registers have made it possible to highlight that the dispersion of asbestos fibers in the outdoor environment was the only ascertained cause of mesothelioma in subjects from asbestos-cement factories, from the Balangero mine (Piedmont Region), from some serpentine rock quarries with tremolite outcrops in the Southern Apennines and in Alta Val di Susa (Piedmont Region); from chrysotile and serpentine caves in Valmalenco (Lombardy Region). Furthermore, cases of pleural mesothelioma were clearly caused by environmental pollution from fluoroedenite fibers in Biancavilla (Sicily Region). On the other hand, regional mesothelioma registers have also reported other circumstances of environmental asbestos exposure, like in the case of steel industry, shipbuilding, chemical plants, railway lines, and repair/demolition of railway carriages. However, these reports have not found confirmation on the basis of ad-hoc studies and it is likely that there is a lack of homogeneity in the assessment of individual cases. Apart from the scenarios which have been the subject of ad-hoc studies, the assessment of the causal role of environmental exposure to "in place" asbestos in the onset of pleural mesothelioma is problematic without an effort to more carefully examine the circumstances of possible exposure, harmonization of the attribution criteria used in the individual regional registers, analytical assessment of the impact of such exposure on the risk of onset of mesothelioma.

[Death certification of pleural malignant mesothelioma from the Italian National Institute of Statistics: a comparison on 269 clinical diagnosis confirmed at autopsy (1997-2016)]. / La certificazione Istat di decesso per mesotelioma maligno pleurico: comparazione con 269 diagnosi cliniche confermate all'autopsia (1997-2016).

OBJECTIVES: To evaluate the agreement between pleural malignant mesothelioma diagnosis in life, with diagnoses confirmed at autopsy, and the certification of the cause of death in the form of the Italian National Institute of Statistics (Istat). DESIGN: comparison between autopsic cases and cases from Istat. SETTING AND PARTICIPANTS: two series of autopsy diagnoses of pleural malignant mesothelioma placed from 1997 to 2016; 185 in shipyard workers and 90 in Brescia province inhabitants, for whom the Istat death form was acquired for 180 and 89 subjects, respectively. RESULTS: the general agreement between pleural malignant mesothelioma clinical diagnosis in life and death certification was about 91% for the first group and 92% for the second one. In the first group, the age at diagnosis does not affect the accuracy of the death certification, which instead increased over time to become total in the period 2010-2016. CONCLUSIONS: the study suggests that the agreement between pleural malignant mesothelioma clinical diagnosis and certification of the cause of death appears to be very high.

Is Mesothelioma Unrelated to the Lung Asbestos Burden? Comment on Visonà et al. Inorganic Fiber Lung Burden in Subjects with Occupational and/or Anthropogenic Environmental Asbestos Exposure in Broni (Pavia, Northern Italy): An SEM-EDS Study on Autoptic Samples. Int. J. Environ. Res. Public Health 2021, 18, 2053.

We read with interest the report by Visonà and coworkers on the lung asbestos fiber burden in an autopsy series of decedents from mesothelioma (MM: 59 cases) and individuals who "suffered from asbestosis and died of its complications" (13 cases) [...].

[Biological risk from SARS-CoV-2 and respiratory protection device for health workers during the first pandemic phase: a scenario that had to be avoided]. / Rischio biologico da SARS-CoV-2 e dispositivi di protezione respiratoria per gli operatori sanitari e assistenziali nella prima fase pandemica: uno scenario che doveva essere evitato.

In Italy, the SARS-CoV-2 pandemic showed the devastating consequences of a widespread biological risk not only for the general population, but also for healthcare workers that diagnose COVID-19 and treat patients. In the set of preventive measures taken to reduce this contagion, a fundamental role in personal protection is played by equipment suitable for preventing the contaminated air inhalation. Despite this severe biological risk during the first epidemic phase, some institutional operating protocols and recommendations have shown limitations and contradictions and, therefore, they must not be repeated. It was observed a widespread inadequate use of respiratory protections, such as surgical masks, which show a low efficacy for health workers; adequate respiratory protective devices are instead rarely used, while their use should have been guaranteed more extensively than it is recommended and noticed, according to the current work hygiene legislation.

Diagnosis of lung cancer: a necropsy-based study of 128 cases (1997-2016).

BACKGROUND: The diagnosis of lung cancer (LC) may be difficult to make in the elderly. We report on the diagnostic elements available in life in an LC necropsy case series of asbestos-exposed workers and describe the frequency of non-neoplastic asbestos-related diseases as biological exposure indices. METHODS: We reviewed pathologic and clinical records of an unselected series of autopsies (1997-2016) in patients with LC employed in the Monfalcone shipyards. We assessed the consistency with autopsy results of diagnoses based on, respectively, radiologic, cytologic, and histologic findings. RESULTS: Data on 128 autopsy-confirmed LC cases were available; in life, 119 had been diagnosed as LC. Among these, 49 had histologic confirmation of diagnosis (17 with immunophenotyping); histology had been negative in 4. Cytology had been the main positive finding and the basis for diagnosis in 24 cases, but had been negative in 13. Chest computed tomography had been the basis for diagnosis in 45; in 18 cases, it had been negative. Nine patients had received a diagnosis different from LC, among whom 4 had been suspected to have malignant pleural mesothelioma by chest computed tomography. Pleural plaques were found in 124 and histologic asbestosis in 46 cases. CONCLUSIONS: Autopsies confirmed all LC diagnoses received in life, including 46 that would have been considered only possible LC based on clinical workup. The overall survival in this case series was poor. The high prevalence of pleural plaques and asbestosis suggest severity of asbestos exposures.

[Asbestos exposure and related diseases among friction products workers (1971-2016)]. / Esposizione ad amianto e patologie correlate in addetti alla produzione di materiali di attrito (1971-2016).

SUMMARY: Worldwide studies have been published on the mortality of workers employed in asbestos-based materials for the production of clutches and brakes. However no one of these studies is related to Italian cases. Furthermore, not even surveys have been conducted in Italy to characterize the correlation between asbestos exposures and the possible occurring of asbestos-related disease. Our objectives are the following: i) to assess and quantify the asbestos exposure cases, ii) to describe the nature and the frequency of asbestos-related diseases among blue collar employees of an important factory producing brakes and clutches with chrysotile asbestos content from 1971 to 1993 and iii) to provide preliminary data on cumulative asbestos exposure estimated using lung fibre burden analysis. Critical appraisal of airborne asbestos fibre measurements and identification of cases of asbestos-related diseases between the blue collar employees, either notified to the local health authority or recovered from the Italian national Mesothelioma registry was investigated. Lung fibre burden analysis using the lung tissue samples from two deceased blue collar employees was also performed. Airborne asbestos fibre measurements (carried out in 1982) suggested asbestos fibres average concentrations of about 0.3 f/ml, while all 1992 measurements showed results below 0.1 f/ml. Furthermore, since 1988, we identified four cases of pleural plaques, three cases of asbestosis and seven cases of lung cancer. No case of malignant mesothelioma was found. In both lung cancer cases, analysed to measure the lung fibre burden, commercial amphiboles were absent or in limited concentration but chrysotile and, especially, tremolite asbestos were present in noticeable amount. In conclusion, since 1971 and up to early 1980s, exposure to chrysotile asbestos and talc, likely contaminated by tremolite, had been significant and comparable to levels causing asbestosis long-term risk. No case of malignant mesothelioma was found, that is consistent with the absence of amphiboles and with the lower risk of mesothelioma associated with the chrysotile asbestos. However a subset of the blue collar employees, the ones employed later on, could still have not reached the full risk condition, and so being still at risk of developing malignant mesothelioma. In the two lung cancer cases studied, the lung fibre burden was essentially made of chrysotile and tremolite. Lastly, lung cancer occurrence in the population of blue collar employees has been likely underestimated and the correct determination of lung cancer risk should be done through the mortality analysis of this population.

Severe silicosis due to diatomaceous earth in dental alginate: a necropsy study.

BACKGROUND: Severe silicosis from occupational exposure to calcined diatomaceous earth has been observed in the past, due to the high-temperature transformation of amorphous silica in crystalline phases, mainly cristobalite. In dental alginate production and use a silica exposure may be underestimated. OBJECTIVES: To describe the clinical picture, the scenario and pattern of occupational exposure to silica and the corresponding necroscopic findings of a case of silicosis in a worker engaged in the production of alginates for dental use. METHODS: A commercial sample of calcinated diatomaceous earth and necroscopic lung samples were analysed by scanning electron microscopy (SEM-EDS) and X-ray diffraction (XRD) for the quali-quantitative determination of crystalline silica. Material safety data sheets (MSDSs) of diatomaceous earth produced in 2002 and 2018 were examined to assess the information content on silicosis risk. Clinical findings and post-mortem examinations of the worker are evaluated. RESULTS: A cristobalite concentration of 36% (wt/wt) was determined in the diatomaceous earth sample and a large amount of diatom fragments were observed in lung samples. The DRX spectra indicated the presence of cristobalite either in the bulk sample or in the lung tissues. The MSDS dated 2002 reported the presence of SLC up to 63% with cristobalite concentrations minor of 60%, and the resulting risk of silicosis, while the MSDS dated 2018 and referred to a commercial product currently on the market indicated a concentration of cristobalite minor of 1% and no risk of silicosis. The worker was suffering from a severe silicosis, histologically confirmed by necropsy. CONCLUSION: The present case-study revealed that the risk of silicosis from calcined diatomaceous earths used to produce dental alginates has been ignored. The lack of engineering controls and personal protection measures led to a high cristobalite lung burden, consistent with the development of a severe silicosis that were a contributing factor of death. A MSDS of a commercial product currently on the market does not report this serious hazard.

[About the asbestos and the Position Paper on asbestos of the Italian Society of Occupational Medicine]. / A proposito dell'amianto e del Position Paper della Società italiana di medicina del lavoro sull'amianto.

The SIML Position Paper dedicated to asbestos (PPA) is addressed (mainly) to competent practitioners (CP) for the purposes to provide a guidance about a set of items classified as markedly interesting: the actuality of asbestos exposure and the evaluation of the related risk; the diagnosis of the asbestos related diseases; the shape of the risk functions (namely about mesotheliomas); the causal relationship between exposure and disease; the medical surveillance of the workers currently and previously exposed. The scientific literature doesn't acknowledge the idea that nowadays in Italy the frequency of pleural mesotheliomas deriving from environmental asbestos from outdoor sources exposures is really a relevant item. Inside the SIML PPA the chapter concerning industrial hygiene and environmental monitoring themes shows inaccuracies and deficiencies, so resulting of scarce utility for the CPs that should be called for a more cooperative role in front of the employers. The arguments of the diagnosis of the asbestos related diseases is developed with an undue emphasis upon the differential histological diagnosis of asbestosis and, especially, of pleural mesothelioma: nosographic aspects that hardly are posed to the attention of the CP. A similar emphasis is posed towards the shape of the risk function for pleural mesothelioma, a theme absent from the current practice of the CP such as of other occupational practitioners. In conclusion, next to themes of undoubted interest for the PC, the SIML PPA dwells on the scrutiny of some topics representing critical elements of the current contrast between consultants and valuers in the context of criminal prosecutions: subjects having forensic relevance but far from the "application actuality" for the CP invoked in the PPA. A greater transparency, last but not least, was to have been posed, inside the SIML PPA, in the disclosure of the conflict of interests (COIs) of some Authors, declaring their consultancy in favour of companies.

Lung Asbestos Fibre Burden and Pleural Mesothelioma in Women with Non-occupational Exposure.

BACKGROUND: Malignant pleural mesothelioma (MPM) due to environmental and familial (domestic) asbestos exposure is well recognized. However, information on cumulative asbestos dose in subjects affected by MPM is limited. OBJECTIVES: To evaluate the residual lung asbestos fibre and asbestos body burden in women with MPM with past environmental and/or familial asbestos exposure. METHODS: We collected lung samples from autopsies regarding 15 non-occupationally asbestos-exposed MPM cases, divided in three groups: (i) familial exposure from the Fincantieri shipyards in Monfalcone (No. 7), (ii) environmental and familial asbestos exposure from the asbestos-cement plant Fibronit in Broni (No. 6), and (iii) environmental exposure from the Fibronit plant (No. 2). Asbestos body (AB) and fibres (AF) per gram of dry lung tissue were counted by optical and scanning electron microscopy, respectively, and expressed as geometric means and standard deviations (GM, GSD). RESULTS: GM/GSD of AB counts were 6123/9.6 (Group 1), 13 800/10.4 (Group 2), and 8400/1.1 (Group 3); GM/GSD of AF were 0.6/2.1 (Group 1), 7.9/2.1 (Group 2), and 6.0/2.3 (Group 3) million. Pleural plaques were observed in 12 cases. CONCLUSIONS: Exclusive familial exposure to asbestos determined cumulative doses close to those observed in moderate occupational exposure circumstances. Our results also suggest that combined environmental and familial exposures may cause unexpectedly high cumulative fibre doses.

Relationship between pleural plaques and biomarkers of cumulative asbestos dose. A necropsy study.

BACKGROUND: The relationship between pleural plaques and cumulative asbestos exposure is controversial. OBJECTIVES: To evaluate the relationship between lung asbestos bodies (AB) and fibres (AF) and plaques presence and extension. METHODS: In a necropsy series of shipyard workers with asbestos-related diseases, we measured counts (per g of dry lung tissue) of AB (thousands) and AF>1 µm (millions). Pleural plaques were classified into three extension grades. We fitted univariate and multivariable linear (dependent variables: AB and AF, log10 transformed) and multinomial (dependent variable: plaques grade) regression models. RESULTS: We analysed 124 subjects, 13 without plaques 20 with grade 1, 69 with grade 2, and 22 with grade 3 plaques. Geometric means (GM) of AB were 10.6, 23.3, 126, and 140 in the four groups respectively (P=0.0001). GMs for AF (mostly amphiboles) were 1.2, 1.4, 7.3, and 12.9 (P=0.0001). AB and AF were strongly correlated (r=0.81). The likelihood of no plaques and grade 1 plaques decreased with increasing AB and AF doses, with a corresponding increase of grade 2 and 3 plaques. Plaque presence and extension was also associated with histologically verified asbestosis (P<0.001). CONCLUSIONS: Our study showed a strong positive relationship between pleural plaque presence and extension and both lung asbestos burden and asbestosis.

On the diagnosis of malignant pleural mesothelioma: A necropsy-based study of 171 cases (1997-2016).

BACKGROUND: Malignant pleural mesothelioma (MPM) diagnosis is known to be difficult. We report on the diagnostic elements available in life in an MPM necropsy case series and describe the frequency of non-neoplastic asbestos-related diseases as biological exposure indices. METHODS: We reviewed pathologic and clinical records of an unselected series of autopsies (1977-2016) in patients with MPM employed in the Monfalcone shipyards or living with shipyard workers. We assessed the consistency with autopsy results of diagnoses based on, respectively, radiologic, cytologic, and histologic findings, with and without immunophenotyping. RESULTS: Data on 171 cases were available: for 169, autopsy confirmed the MPM diagnosis. In life, 119 cases had histologic confirmation of diagnosis, whereas 7 were negative; all cases without immunophenotypization were autoptic MPMs. Cytology alone had been positive in 18 autoptic MPM cases, negative in 14. Radiologic imaging alone had been positive in another 16, negative in 11. In the 2 cases not confirmed at autopsy, MPM had been suspected by chest computed tomography only. Bilateral pleural plaques were found in 144 and histologic evidence of asbestosis in 62 cases. CONCLUSIONS: Autopsies confirmed 169/171 cases, including cases that would not be considered as certain based on diagnosis in life. Radiologic imaging, cytologic examination of pleural effusions, or both combined had low sensitivity but high positive predictive value: when they are positive, proceeding to thoracoscopy should be justified. MPM has been correctly diagnosed even without immunohistochemistry. The prevalence of pleural plaques and asbestosis was high due to severity of asbestos exposures in these cases.

Pleural mesothelioma in doll manufacture: possible asbestos exposure. / Mesoteliomi pleurici in addette alla fabbricazione di bambole: esposizione ad amianto?

BACKGROUND: The occurrence of malignant mesothelioma is almost always causally associated to asbestos exposure but, considering women occurrences, this association is often difficult to demonstrate and consequently the asbestos exposure is defined as 'unknown'. OBJECTIVES: To describe the working activity and to give occupational asbestos exposure probability estimation related to an uncommon and poorly investigated productive sector: doll manufacture. METHODS: From the Province of Brescia Mesothelioma Registry, established in 1993 on population-based criteria, we have extracted the certified mesothelioma diagnosis cases, related to patients who were employed for some time in doll manufacture. RESULTS: Among the 757 total cases of malignant mesothelioma registered and studied up to 2016, we found 3 cases of pleural epithelial mesothelioma histologically diagnosed in young women who had worked in two doll manufacturing companies and whose asbestos exposure had been initially defined as 'unknown', because an environmental, family or extra-professional asbestos exposure was considered unlikely. However, the judicial autopsy performed on one of the 3 women had allowed examining lung tissue samples with Scanning Electron Microscopy. This technique showed a concentration of amphiboles fibers of about 12,000,000 per gram of dry lung tissue, with a consequent re-classification of asbestos exposure from 'unknown' to 'occupational certified'. DISCUSSION: Mesotheliomas in women with no apparent occupational asbestos exposure are normally referred to life or family environmental exposure. Moreover, it is known that occupational asbestos exposure in women is difficult to recognize. Previously, only one publication had reported two cases of mesothelioma in cloth doll manufacture. The occurrence of two mesothelioma cases in the same company out of the three here presented was suggesting an occupational exposure. The finding of a high amphibole fibers lung concentration confirmed the previous hypothesis, despite the impossibility to determine the circumstances with good evidence. CONCLUSION: The three cases of mesothelioma in doll production workers suggest that also in this restricted manufacturing sector had occurred an occupational asbestos exposure, which is up to now unknown and isn't due only to the use of sewing or ironing machines. The lung asbestos fibers burden analysis is confirmed to be a decisive factor in the assessment of mesothelioma cases with 'unknown' exposure.

Residual fibre lung burden among patients with pleural mesothelioma who have been occupationally exposed to asbestos.

OBJECTIVES: To evaluate the lungs asbestos fibres concentration in participants with malignant pleural mesothelioma (MPM) who have been occupationally exposed. METHODS: The lung samples were obtained from pleuropneumonectomies or autopsies of 271 male MPMs. The lung samples were examined through scanning electron microscopy. Retrospective assessment was used to assess for asbestos exposure. This study includes 248 MPMs with an occupational exposure defined as either 'definite' or 'probable' or 'possible'. RESULTS: The participants had finished working in asbestos exposure conditions more than 20 years ago (on average 26.1±11.0 years). The fibre burden resulted with a geometric mean equal to 2.0 (95% CI 1.6 to 2.4) million fibres per gram of dry lung tissue. The burden was higher among participants employed in asbestos textiles industry and in shipyards with insulation material, if compared with construction workers or non-asbestos textile workers or participants working in chemicals or as auto mechanics. 91.3% of MPMs had a detectable amount of amphibole fibres. A strong lung clearance capability was evident among workers exposed to chrysotile fibres. Owing to that, the 1997 Helsinki Criteria for occupational exposure were reached in <35% of cases among participant working in construction, in metallurgical industry, in chemical or textile industry and among those performing brake repair activities. CONCLUSIONS: The MPM cases are now occurring in Italy in participants who ceased occupational asbestos exposure decades before the analysis. A large majority still shows a residual content of amphibole fibres, but given the lung clearance capability, attribution to occupational exposure cannot rely only on fibres detection.