Cancer Mortality in Merchant Seamen

Cancer mortality excess has been reported repeatedly over the past hundred years to occur in merchant seamen. More recently lung cancer has been found to account for some of this excess and the question of the contribution made by cigarette smoking raised. In the one study where there was some information on smoking habit, it did not appear that cigarettes would have accounted for all the excess cancer observed. In other mortality studies, where excess cancer mortality was observed, the other cigarette-linked causes of death were not prominent. In a preliminary mortality analysis of a small population of merchant seamen, two cases of malignant mesothelioma have so far been identified, and in a national mesothelioma register 28 cases have been reported in seamen: both instances constitute abnormal occurrences. The presence of substantial amounts of asbestos-containing materials in naval construction which are continuously subjected to vibration and intermittently disturbed during servicing, and the detection of radiological stigmata consistent with asbestos exposure, add plausibility to the hypothesis that occupational asbestos exposure contributes to the apparent excess cancer mortality in merchant seamen. Methodologic deficiencies in epidemiologic studies reported to date make for uncertainty. Properly designed studies will be needed to quantify disease excess and to identify potentially causal associations. Even in the absence of such data it would be prudent to contain the asbestos currently installed and to promote smoking cessation programs.