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December 2, 1974

Isoniazid and Cancer Risks

Author Affiliations

University of Ottawa Ottawa

JAMA. 1974;230(9):1254. doi:10.1001/jama.1974.03240090014005

To the Editor.—  The report on the effectiveness of isoniazid in preventing clinically manifest tuberculosis (229:528, 1974) did not take into account the potential carcinogenicity of the drug. Isoniazid-induced leukemia and tumors in laboratory animals cannot be generalized to man, but they justify careful scrutiny of the potential risk.An increase over expected numbers of deaths due to neoplasms in male tuberculosis patients treated with isoniazid has been observed, although the relative risk (1.4) was not significant statistically.1 In one section of the randomized trials of the Public Health Service, mental patients under intensive care who had received isoniazid prophylactically experienced a higher rate of death due to neoplasms than did the control group on placebo.2 The increase in neoplasia was not observed in other test populations. This discrepancy has not been clarified, but it is conceivable that the group under intensive care actually took the prescribed dose