Chlorambucil-induced chromosome damage to human lymphocytes is dose-dependent and cumulative.

Sister chromatid exchanges (SCEs), a sensitive measure of chromosome damage, were counted in peripheral-blood lymphocytes from 10 patients with Behcet's syndrome receiving chlorambucil. All patients had abnormal counts. Damage was related to both daily dose and duration of therapy and was occurring at a greater rate than its repair. The patient who had been treated the longest and had received the highest total dose also had the highest SCE count. He died from acute leukaemia. SCE analysis may provide a method for detecting patients at risk from oncogenic effects of cytotoxic drugs.