Transformation of lymphoma to amyloidoma following radiation therapy.

A 62-year-old man presented with a localized upper-extremity small cell lymphoma with plasmacytoid features and an associated IgM lambda serum immunoglobulin level of 1,730 g/dl. The tumor was treated with 5,960 rad over 47 days. On completion of radiation therapy, the tumor had regressed only minimally, and the monoclonal immunoglobulin level had decreased by 63 per cent; repeat biopsy revealed that the lymphoma had been replaced by a virtually acellular mass of amyloid. It is postulated that radiation therapy accelerated the tissue conversion of lambda light chain into the beta-pleated sheet structure characteristic of amyloid fibrils.