The oncogenicity of chlorambucil in rheumatoid arthritis.

Chlorambucil is useful in patients with rheumatoid arthritis (RA) refractory to other agents but there is concern about the risk of haematological malignancy with this agent. A retrospective survey was performed to assess the incidence of all types of malignancy in 39 patients treated with chlorambucil (mean daily dose 4.25 mg, mean duration of treatment 25 months). These patients were compared with 30 patients with RA who received contemporaneously, the purine analogues azathioprine or 6-mercaptopurine (mean dose 100 mg, mean duration of treatment 24 months). Eight patients treated with chlorambucil and one patient receiving purine analogues developed cutaneous malignancy (p = 0.03). In the chlorambucil-treated patients these were mostly multiple and recurrent. Three patients treated with chlorambucil developed myeloid leukaemia or a preleukaemic state, whilst no patient treated with purine analogues developed this complication. The use of chlorambucil in RA is associated with an increased risk of cutaneous as well as haematological oncogenesis.