Immune hemolytic anemia induced by 6-mercaptopurine

BACKGROUND: Myelosuppression is the main hematotoxic effect of 6-mercaptopurine (6-MP), which is an antimetabolite chemotherapy drug. Immune hemolytic anemia associated with this drug has not been previously reported. CASE REPORT: A 67-year-old man with chronic myelomonocytic leukemia presented with anemia 2 weeks after 6-MP therapy had been initiated. Additional tests provided laboratory evidence of hemolysis. When treatment was stopped, the patient's condition and laboratory results showed a progressive improvement. RESULTS: The direct antiglobulin test was positive for IgG. The eluate and the serum were not reactive with panel red cells but reacted with 6-MP-treated red cells, while the normal serum pool was unreactive. The direct antiglobulin test was no longer positive by 20 days after the cessation of 6-MP therapy. CONCLUSION: This drug, 6-MP, should be added to the list of drugs that have been reported to cause immune hemolytic anemia by means of the so-called hapten mechanism.