The systemic carcinogenicity of iron‐dextran has been investigated after single and repeated injections of Imferon in mice and rats. Systemic iron deposits induced by irondextran resulted in a stepwise development of reticulosarcomas. Such a histologic reaction, however, was not seen in relation to iron deposits following iron‐carbohydrate complex (Intrafer) administration. Distant tumours arising in the lymphoreticular structures showed a uniform latency in test and control mice, while tumours of other origin showed a prolonged latency as compared to such tumours in control animals. It is suggested, therefore, that iron‐dextran may act as a co‐carcinogenic factor in the case of lymphoreticular neoplasia, increasing host susceptibility to the oncogenic virus presumably present in both control and test animals. The non‐lymphoreticular distant and local tumours may stem from a different and direct carcinogenic action of iron since these tumours showed a prolonged latency and were seen after the administration of either iron‐dextran or iron‐carbohydrate complex. The results indicate an inconclusive dose‐response relationship, though no significant difference was found between tumour yield in the larger groups receiving 500 and 25 mg Fe…/kg body weight, the latter dose being within the therapeutic level on a comparative weight basis. Copyright © 1968 Wiley‐Liss, Inc., A Wiley Company
