Not surprising given the pathophysiology. "stopping exposure does not materially modify the subsequent risk of mesothelioma"

http://www.ncbi.nlm.nih.gov/pubmed/22314851

Eur J Cancer Prev. 2012 Feb 5. [Epub ahead of print]
Role of stopping exposure and recent exposure to asbestos in the risk of mesothelioma.
La Vecchia C, Boffetta P.
Source
aDepartment of Epidemiology, 'Mario Negri' Institute for Pharmacological Research bDepartment of Occupational Health, University of Milan, Milan, Italy cInternational Prevention Research Institute, Lyon, France dThe Tisch Cancer Institute, Mount Sinai School of Medicine, New York, New York, USA.

Abstract
The model of asbestos-related mesothelioma implies that the time since first exposure (latency) is the key determinant of subsequent risk. The role of recent exposure or stopping asbestos exposure, if any, is, however, open to discussion. A literature review was conducted to the end of 2010. In a cohort of 1966 Italian textile workers, the standardized mortality ratio, on the basis of 68 deaths from mesothelioma, was 6627 for workers employed only under the age of 30 years, 8019 for those employed both under the age of 30 years and at the age of 30-39 years, and 5891 for those employed both under the age of 30 years and at the age of 40 years or more. In a cohort of Italian asbestos cement workers, including 135 deaths from pleural cancer, compared with workers who had stopped exposure for 3-15 years, the relative risk (RR) was similar for those still employed (RR=0.67) and for those who had stopped for 30 years or more (RR=0.65). In a British case-control study, including 622 cases of mesothelioma and 1420 population controls, the RR substantially increased with increasing duration of exposure under the age of 30 years, but not with exposure at the age of more than 30 years. In the Great Britain Asbestos Workers Survey, including 649 deaths from mesothelioma compared with workers who were still employed and or had stopped for less than 10 years, the multivariate RRs were 0.90 10-20 years after stopping exposure and 0.99 both 20-30 and more than 30 years after stopping. There is consistent evidence showing that, for workers exposed in the distant past, the risk of mesothelioma is not appreciably modified by subsequent exposures, and that stopping exposure does not materially modify the subsequent risk of mesothelioma.