Response to “Lung Cancer Risk Among Non-Smoking Firefighters”
To the Editor:
We thank Drs Guidotti and Goldsmith for their interest in our article. While we agree that this study does not rule out an elevation of lung cancer risk for non-smoking firefighters, there are, however, some misconceptions in the letter that we would like to bring to the reader's attention.
Our results are based on pooled general population case-control studies (not a cohort study as implied by the letter), and the total number of firefighters in the study was 190 (86 cases, 104 controls), whereof only 29 were never smokers, that is, two cases and 27 controls. In the Discussion of our study, we acknowledge the limited statistical power to detect moderate excess risks in the sub analyses. Also, as discussed, we were not able to take into account precise work tasks. Although we knew the years when each firefighter worked, the numbers were too small to stratify the analyses by period of employment.
The SYNERGY project has previously demonstrated that even relatively weak associations (e.g., bricklayers and miners) can be detected in this pooled dataset of population based case-control studies, irrespective of the high prevalence of smokers.1,2 Given accurate information on age and detailed information on tobacco smoking habits confounding by these risk factors is of lesser concern than in most other studies.3
The working group of the pertinent International Agency for Research on Cancer (IARC) Monograph on carcinogenic risks of firefighters classified occupational exposure as a firefighter as possibly carcinogenic to humans (Group 2B), largely on the basis of limited evidence for an increased risk of non-Hodgkin lymphoma, testis and prostate cancer.4 Based on data published in 2007, however, the evidence for lung cancer was inconclusive. The varying tasks and variable exposure levels between different types of firefighters combined with the crude exposure assessment probably contributed to non-differential exposure misclassification that may have resulted in bias towards the null.
Certainly, firefighters may be exposed to established carcinogens, such as polycyclic aromatic hydrocarbons and diesel motor exhaust. Recognition and compensation of occupational cancer depends on the national (or state) legislation, with some countries compensating IARC 2A agents (e.g., in Denmark, under certain conditions), while other countries requiring evidence beyond an IARC Group 1 classification (e.g., doubling of risk).
Our study of firefighters in the SYNERGY consortium is part of a larger project funded by AFA Insurance in Sweden: “Cancer in firefighters—epidemiological studies on cancer risk and assessment of exposure to carcinogens by airways and skin.” This includes three ongoing studies: two epidemiological studies of cancer risk among firefighters in Sweden and one exposure measurement study to evaluate the exposure to some carcinogenic substances by airways and skin contact for firefighters and police forensic investigators in Sweden. The results are expected in 2017 to 2018.