Mesothelioma risk after 40 years
since first exposure to asbestos
Background The risk of malignant mesothelioma (MM) increases
proportionally to the cumulative exposure, and to the 3rd or 4th power of time
since first exposed, to asbestos. However, little is known about the risk of MM
after more than 40 years since first exposure because most epidemiological
studies do not have follow-up for sufficient periods of time.
Methods The data from six cohort studies of exposed workers
and two cohorts with residential exposure have been pooled. A nested case
control design matched cases and controls on calendar period and age.
Conditional logistic regression modelled the relationship between time since
first exposure and risk of MM.
Results The combined data consisted of 22 048 people with
asbestos exposure (5769 women), 707 cases of pleural MM (165 in women) and 155
cases of peritoneal MM (32 in women). Median time since first exposure for
pleural MM cases was 38.4 years (IQR 31.3–45.3). Median duration of exposure
for pleural MM cases was 3.75 years (IQR 0.7–18.2). The rate and risk of
pleural MM increased until 45 years following first exposure and then appeared
to increase at a slower power of time since first exposure. The rate of
increase in peritoneal MM over the 10–50 years since first exposure continued
to increase.
Conclusions Exposure to asbestos confers a long-term risk of
developing pleural and peritoneal mesothelioma which increases following
cessation of exposure. While the rate of increase appears to start to level out
after 40–50 years no one survives long enough for the excess risk to disappear.