Chronology of asbestos cancer discoveries: experimental studies of the Saranac Laboratory.

This commentary challenges a recently published perception that Dr. Le Roy Upson Gardner had not actually discovered in 1942 that inhaled chrysotile fibers could induce malignant neoplasia in mice. The handwritten laboratory notes and some of Dr. Gardner's slides have recently been found. They verify that the tumors he saw in the mice included truly malignant neoplasms. Gardner had by then also accumulated 11 cases of human lung cancer (two mesotheliomas) derived from Quebec asbestos miners and millers. An inhalation study designed by Dr. Gardner and conducted between 1951 and 1954, using cancer-insusceptible mice, yielded neoplasia risk ratio of 5.7 compared with control animals. The studies also showed that the primary effect of chrysotile is to cause epithelial proliferation in alveoli adjacent to bronchioles. Chrysotile type asbestos bodies were shown to remain only transiently ferruginous, but even though invisible in direct light they can be visualized at high magnification through use of phase contrast and polarized light micrography.