Endocardial Tumors in Rats Exposed to Durable Fibrous Materials

: Endocardial tumors in the rat found in association with intrathoracic implantation of durable fibrous materials are reported here for the first time. In Osborne-Mendel female rats, endocardial tumors occurred in 3 of 50 rats associated with the implantation of fiberglass greater than 5 micron in length and 1-3 micron in diameter, in 1 of 15 rats associated with fiberglass of 0.03 X 3 micron, and in 1 of 15 rats associated with pulverized glass fiber. The intrathoracic administrations of pulverized chrysotile, of cigarette smoke condensate and crocidolite, and of coarse cotton lint, and of intravenous injections of air particulate extract were associated with endocardial tumor in 1 of 15 rats each. The dimensions of the durable fibers associated with endocardial tumors were similar to those of carcinogenic asbestos. Endocardial tumors were not observed in concurrently studied control rats.