Demonstration of clonal selection in a child with non-Hodgkin's lymphoma.

A 2-year-old boy with B-lineage non-Hodgkin's lymphoma is described. He presented with growing skin tumors on his head, and biopsy specimens showed a malignant lymphoma of diffuse lymphoblastic type. Sixty-four percent of bone marrow cells were replaced with lymphoblasts, and they expressed B-lineage markers (CD19 and HLA/DR). Southern blot analysis demonstrated immunoglobulin heavy chain gene rearrangements (two rearranged and one germline) with the germline configuration of the T-cell receptor beta chain gene. Ten months later he relapsed with blasts of M5 morphologic type and a myeloid phenotype with the germline configuration of the immunoglobulin genes. During the next 2 months, myeloid blasts with immunoglobulin gene rearrangement which was identically rearranged with one of the two rearranged bands detected at diagnosis appeared. The most likely explanation for these findings is that initially the patient seemed to have at least two different clones of blasts, and clonal selections occurred during the treatments.