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)