WESTERN Australian researchers have determined the risk of developing mesothelioma continues to increase even 40 years after a person's first exposure to asbestos.
The Curtin University and UWA School of Public Health study is one of the first of its kind and investigated 22,048 people exposed to asbestos across the globe using data from six cohort studies of exposed workers and two of residential exposures.
Pleural and peritoneal mesothelioma are cancers that develop on the lining of the lungs and are almost always caused by asbestos exposure.
Researchers used conditional logistic regression to model the relationship between the time since first asbestos exposure and the risk of pleural mesothelioma and the rarer peritoneal mesothelioma.
They found the rate and risk of pleural mesothelioma increased until 45 years after the first exposure. After 45 years the risk rate then appeared to slow down.
However, the rate of peritoneal mesothelioma over 10-50 years continued to increase.
Curtin University Associate Professor and lead author Alison Reid says the study is important because it examines the long-term impacts of asbestos exposure and further highlighted the dangers of asbestos.
"There have been so few studies on the long-term risk of mesothelioma because most cohort studies don't have follow-up over such long periods of time, therefore it hasn't been possible to look at the long-term risks before," she says.
"The risk of mesothelioma does not appear to decline over time and this stresses that the need to prevent people being exposed to asbestos is paramount."
Patients traced from employee records
A/Prof Reid says the cohort studies chosen had been established many years ago from the employment records of the various companies the workers worked for.
"Over many decades the workers were matched to cancer and death registries in Australia and Italy," she says.
"For example the Wittenoom workers were all employed at some stage by the Australian Blue Asbestos company during its operation of the blue asbestos mine and mill at Wittenoom between 1943 and 1966.
She says they weren't sure what they would find with this study but were surprised when they found the risk of developing peritoneal mesothelioma didn't slow down at all over the extended time span.
"When examined separately some of the cohort studies suggested that the risk of pleural mesothelioma might decline around about 40 years, but in this study we had a lot more cases to examine this issue," she says.