We studied exposure to
asbestos,
pulmonary fibrosis, fiber count, and fiber size in relation to the lobar origin of
lung cancer in 90 consecutive patients. Among the 32 patients with a history of occupational exposure to
asbestos, 22 were construction workers. The proportion of lower-lobe
tumors increased with the duration of exposure from 45% in those working less than 15 years to 82% in those working 15 years or more in the construction trade, as compared with 25% in patients who were probably not exposed. The location of the
tumor in the lower lobe was explained by the high number of total fibers [odds ratio (OR) = 9.0, CI = 2.3-34.6), of fibers 3 microns and longer (OR = 22.1, CI = 3.9-125), and fibers of
anthophyllite (OR = 14.6, CI = 2.4-83.4) and
crocidolite (OR = 7.0, CI = 1.2-41.2) when the effect of smoking and
fibrosis was adjusted in the logistic regression analysis. The location of the
tumor did not correlate with
fibrosis, pack-years smoked, or the number of short (< 3 microns) fibers. Our findings suggest that
asbestos causes an excess of lower-lobe
tumors at a relatively low exposure level, independently of
pulmonary fibrosis.