AbstractLewis lung carcinoma (LLC) induces a range ofhemopoietic alterations in its murine host including progressive anemia, thrombocytopenia, splenomegaly, neutrophilia, and marrow and splenic myeloid hyperplasia. Concentrations of both pluripotent and committed marrow hemopoietic progenitors is increased and the cycling fraction of granulocyte-macrophage progenitors is accelerated. We have developed a way to study whether these hemopoietic effects become long-term consequences of cancer, using LLC-bearing mice with advanced tumor treated with the antineoplastic agent tiazofurin, 2-β-D-ribofuranosyl-thiazole-4-carboxyamide, NSC 286193 (TZ). LLC mice were treated with a single dose of TZ either 150, 300, or 600 mg/kg, intraperitoneally on day 6 posttumor implant when lung metastases are present and all hemopoietic effects of the tumor are recognizable. Even a single dose of 150 mg/kg of TZ produced a significant survival advantage, and 600 mg/kg resulted in 30% of the animals remaining disease free during a 5-month follow-up. A 6-week treatment schedule was devised, administering TZ intraperitoneally, 600 mg/kg, weekly beginning on day 6. In this group, median survival was not reached after 9 months of follow-up. The only evidence of myelotoxicity produced by intermittent administration of TZ was a mild anemia which was fully reversible 2 weeks after discontinuance of the drug. No difference in white blood cell count, differential count, or platelet count was detected in tumor bearers and controls treated with TZ. Both pluripotent and committed marrow hemopoietic precursors remained unchanged in TZ-LLC, TZ-controb and untreated controls throughout treatment and 2 weeks thereafter. This study demonstrates that TZ-cured LLC mice are suitable to explore late hemopoietic effects of cancer.