A case of IgG lambda lymphoma occurring in a patient with previous IgG kappa lymphoma.

When a patient with non-Hodgkin's lymphoma (NHL) undergoes a relapse, immunological testing of malignant lymphocytes usually shows that the relapse cells are derived from the original tumor clone. We have observed a patient with a B cell lymphoma whose cells bore surface membrane IgG kappa at diagnosis and IgG lambda at clinical relapse 21 months later, during which time he had received multiple-drug chemotherapy. The shift from kappa to lambda light chain expression implies that the patient's apparent relapse was in fact due to the development of a second tumour. This may be another example of cytotoxic drug-induced carcinogenesis in a patient with a lymphoproliferative disorder.