Metronidazole and Cancer

To the Editor.— The recent report by the Mayo Clinic group of an elevated risk of all cancers and of lung cancer among the cohort of 771 women who had received metronidazole (Flagyl) for vaginal trichomoniasis in the years 1960 through 19691prompts this update of follow-up on 2460 patients (2236 female and 224 male) who received the drug in the years 1969 through 1973 from the Kaiser Permanente pharmacy in San Francisco. Beard et al2previously reported no statistically significant increase in the incidence of cancers of all sites or of any site except the lung after about ten to 19 years of follow-up. In three to seven years of follow-up we found 45 cases of cancer, with 33 expected on the basis of the age-sex adjusted incidence among 143 574 pharmacy users.3,4The excess was attributable entirely to cervical cancer, whose association with metronidazole-treated vaginitis