Definitions and Measurement Methods
The influence of dimensional configuration on the induction of carcinogenesis was investigated in rats. Thirty seven experiments were conducted with seven durable fibrous materials at or near the size of asbestos (1332214). Female Osborne-Mendel-rats were exposed to a 40 milligram dose of particles. Rats were followed for 2 years to determine the degree of tumorigenesis. The dimensional distribution of glass, dawsonite (12011766), potassium-octatitanate, silicon-carbide (409212), nickel-titanate (12035391), and aluminum-oxide (1344281) were measured. A minimum of 1,000 particles were tabulated in photo micrographs. There was a relationship between tumor probability and particle distribution for all tested fibers. The particles that were less than 0.25 micrometers (microm) in diameter and more than 8microm long were associated with higher tumor probability. Lesions with high tumor probability were acellular, with an abundance of collagen at the site of implantation; the fine long fibers lay free in the interstitial tissues unaffected by phagocytes. Lesions with low tumor probability were highly cellular, composed of low collagen content with an abundance of macrophages. Nonfibrous particles stimulated collagen deposition without the development of tumors. The authors conclude that collagen itself is not the critical factor in carcinogenesis. Fibers that are fine and long may be more carcinogenic than others because they are not compromised by phagocytic activity.