High-Grade Transformation of Chronic Lymphocytic Leukemia and Low-Grade Non-Hodgkin’s Lymphoma:Genotypic Confirmation of Clonal Identity

Abstract

The abrupt appearance of a high-grade tumor in patients with low-grade malignant lymphoma usually is associated with an accelerated clinical disease course. The high-grade lymphoma may take a variety of histologic forms and often, but not always, represents evolution of the original low-grade disease, as shown by immunophenotypic or immunogenotypic studies. The authors describe the transformation of a variety of low-grade B-cell neoplasms to high-grade tumors in four patients. The initial diagnoses included chronic lymphocytic leukemia and mantle cell lymphoma in one patient each and low-grade follicular lymphoma in two patients. The high-grade tumors were classified as lymphoblastic lymphoma in one patient and small noncleaved cell lymphoma in two patients. The high-grade component manifests primarily in the peripheral blood as circulating blast-like cells consistent with large-cell lymphoma in the remaining patient. In each case, immunophenotypic studies showed identical monoclonal surface immunoglobulin expression on the low- and high-grade tumors. Immunoglobulin heavy chain gene and kappa light chain gene studies showed identical clonally rearranged bands in paired samples from three of the four patients, a finding indicative of clonal identity. Unexpectedly, dissimilar immunoglobulin light and heavy chain gene rearrangements were detected in the paired samples from one patient with previously diagnosed follicular lymphoma, making the relationship of the two tumors from this patient uncertain; however, additional Southern blot analysis of the bcl-2 gene showed identical rearrangements in both lesions. Furthermore, polymerase chain reaction across the t(14;18) major breakpoint region in both tumors amplified nucleotide fragments of identical size, confirming the clonal identity of the low- and high-grade lymphomas despite the divergent immunoglobulin gene studies. These studies show that low-grade malignant lymphomas of small lymphocytic, mantle cell, or follicular small cleaved cell types may assume high-grade morphologic characteristics, that this change is the result of transformation of the preexisting low-grade malignant neoplasm, and that this progression, like typical Richter's syndrome, is associated with a dramatically accelerated clinical course. In addition, these studies confirm previous reports that disparate immunoglobulin light and heavy chain gene rearrangements are not necessarily an indicator of different cellular origins, and additional genotypic studies occasionally may be required to show the clonal identity of the cell population involved in these morphologic transformations.(ABSTRACT TRUNCATED AT 400 WORDS)