Rates of malignant mesothelioma



Rates of malignant mesothelioma

Rates of malignant mesothelioma (MM) have been shown to increase proportionally to cumulative exposure to asbestos and increase with the third to fourth power of time since first exposure to asbestos, when based on observations of 20–40 years latency.1 Little is known about the risk of mesothelioma after more than 40 years following first exposure because most epidemiological studies do not have follow-up for such long periods of time.
Other work has suggested that the increasing risk of mesothelioma observed over the first 20–30 years following first exposure to asbestos may flatten out after more than 40 years since first exposure. Within the Eternit workers cohort the rate of pleural MM increased up to 40 years following first exposure and plateaued thereafter, whereas peritoneal MM showed a continuing increase.2 Among female gas mask workers exposed to crocidolite no cases of MM arose more than 51 years after first exposure.3 Among Turin textile workers a reduction of the MM rate was observed.4 Similarly, the overall rate of MM appeared to level off after 50 years following first exposure in the Wittenoom workers,5 and this was in pleural and peritoneal MM.6Among the former residents of Wittenoom (those who did not work for the asbestos company), high rates of pleural mesothelioma have been observed. These were greatest among those with more than 40 years since first exposure; 165 per 100 000 women and 351 per 100 000 men.7Data from six cohort studies of occupationally exposed workers and two cohort studies of people exposed paraoccupationally and from their general environment was pooled in order to document the rate of MM after >40 years from first exposure.

Methods
Participants came from six occupational cohort studies (five from Italy—Casale Monferrato Eternit workers,8 amosite factory workers from Molina di Ledro, Trento9 ,10 and three railway carriage construction and maintenance workers’ cohorts11) and one from Australia (Wittenoom crocidolite miners and millers12), and two cohorts with general environmental asbestos exposure (one Australian—Wittenoom residents)13 and one Italian (wives of Eternit asbestos cement factory workers14)