Excessive chemotherapy-related granulocytopenia in a child with non-Hodgkin's lymphoma and a congenital abnormality of purine salvage.

A girl with non-Hodgkin's lymphoma and immunodeficiency based on absence of the purine salvage pathway enzyme purine nucleoside phosphorylase experienced profound neutropenia while receiving combination chemotherapy with cyclophosphamide, vincristine, methotrexate, and prednisone (COMP). Neutropenia was most severe following courses that included either systemic or intrathecal methotrexate, even in the face of major dose reductions. Delays in the development of neutropenia-during periods of leucovorin administration also implicate methotrexate as the primary responsible agent. This case suggests that certain immunodeficiency states predispose patients to extensive chemotherapy-induced myelosuppression and supports the concept that purine salvage is a clinically important mechanism for modulating methotrexate toxicity.