Even then, the ISO standard states that “carcinogenicity should be conducted only if there are suggestive data from other sources.” Where implantation does not represent the most appropriate or there is a more practical route of exposure, scientifically justified alternative routes should be considered (Henry, 1985). The intent of such testing is to determine the carcinogenic (“tumorigenic”) potential of devices, materials and/or multiple exposures over a period of the total life-span of the test animal. Such tests are frequently designed to evaluate both the chronic toxicity and the tumorigenicity in a single study as well as device efficacy. These studies are the longest and most expensive of the nonclinical studies typically conducted on any new device or device material. These studies are important because, as noted by the International Agency for Research on Cancer (1987), “in the absence of adequate data on humans, it is biologically plausible and prudent to regard agents for which there is sufficient evidence of carcinogenicity in experimental animals as if they presented a carcinogenic risk to humans.” The best established risks of carcinogenicity have to do with the effects of metals leading from long term implants.