Fischer rats in five experimental groups were given a single i.m. injection of penicillin suspension containing carcinogenic Ni3S2 dust (2.5 mg), alone or in combination with equimolar amounts of aluminum, copper, chromium, or manganese dusts. Rats in five control groups were treated identically, except that the Ni3S2 dust was omitted. After 24 months, the incidence of sarcomas at the injection site was 63% in the group that received the combination of Ni3S2 and manganese dusts, compared with incidences of 96 to 100% in the groups that received Ni3S2 alone or in combination with aluminum, copper, or chromium dusts (p < 0.001). No sarcomas occurred at the injection site in control groups that did not receive Ni3S2. The finding that the addition of equimolar amounts of manganese dust to Ni3S2 dust significantly depresses Ni3S2-induced tumorigenesis provides an experimental system for investigations of metal interactions in carcinogenesis.

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Sponsored by Research Grants EHS C 0109, HSM-99-72-24 from the National Institute for Occupational Safety and Health, and AT(11-1)-3140 from the Atomic Energy Commission.

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