Cadmium and
cadmium compounds are carcinogenic both by inhalation and by injection. For purposes of risk assessment, a prudent public health approach has been that, if a chemical has been demonstrated to be carcinogenic by one route, it should be considered carcinogenic by all routes. This policy has been questioned for several toxic metals including
cadmium. After reviewing the literature on
cadmium carcinogenicity and genotoxicity, we think that
cadmium should be considered noncarcinogenic by the oral route. The bases for this decision included: (1) a database for genotoxicity of
cadmium with more negative test results than positive results and with most positive results in in vitro tests, indicating that
cadmium has limited genotoxicity; (2) some epidemiologic evidence of respiratory tract
cancer and
prostatic cancer in people occupationally exposed to airborne
cadmium but no reliable evidence of
gastrointestinal tract cancers in workers; and (3) a large dietary oncogenicity study in rats of
cadmium chloride at several dose levels, including a maximally tolerated dose (50 ppm) in males, which showed no increase of
tumors due to
cadmium ingestion in all of the 19 tissues examined. The conclusion that an agent, which has been shown to be carcinogenic by one route of exposure, is not carcinogenic by a second route should be made only in the presence of robust data which indicate the lack of effect via the second route of exposure.