CLL-131: Sequential Development of Three Mature Lymphoid Neoplasms in a Single Patient: Clonal Relationship and Molecular Insights

Context Two variants of Richter Syndrome (RS) are recognized, namely the Diffuse Large B-Cell Lymphoma (DLBCL) and the Hodgkin's Lymphoma (HL) variant. Clonal relationship, defined as an identity of the immunoglobulin heavy chain variable (IGHV) region sequence between CLL and RS clones, characterizes patients with a poor prognosis. Objective To describe and molecularly profile the peculiar case of a 63-year-old patient with a CD5+ Monoclonal B-Cell Lymphocytosis (MBL), who sequentially developed a DLBCL-RS followed by a HL-RS. Patients & Methods DLBCL-RS and HL-RS were diagnosed by histological and immunohistochemical evaluation of lymph node sections. Standard IGHV clonality was assessed by Sanger sequencing (SS) analysis. Allele-Specific Oligonucleotide-droplet digital PCR (ASO-ddPCR) with tumor-specific primers was performed to quantitatively investigate the presence of MBL and RS clones during disease evolution. The mutational profiles of MBL and DLBCL were assessed by next-generation sequencing (NGS). Results Three years after the MBL diagnosis, DLBCL-RS developed. Based on standard IGHV clonality analysis, the lymphoma was considered as a de novo DLBCL and treated accordingly, achieving a persistent complete response. Three years later, the patient developed a clonally unrelated HL-RS, refractory to bendamustine, but successfully treated with brentuximab vedotin and radiotherapy. Results from a more sensitive ASO-ddPCR quantitative analysis showed that the RS-DLBCL clone was already present - although undetectable by standard SS - in the peripheral blood at MBL diagnosis, thus deriving from the transformation of a pre-existing CD5+ clone. Both the MBL and DLBCL-RS clones were carrying low-risk genetic features [i.e., del(13q) and hypermutated IGHV], and NGS analysis resulted in negative for all the evaluated mutations, including TP53 and NOTCH1. IGHV clonality analysis, performed by ASO-ddPCR on the lymph node of HL-RS, confirmed its unrelatedness with both MBL and DLBCL-RS. Conclusions In this case, characterized by a high degree of complexity due to the presence of three sequentially occurring neoplastic clones, the application of modern and sensitive molecular technologies uncovered that DLBCL-RS, initially considered as a de novo lymphoma, was instead the result of the transformation of a pre-existing ancillary clone, already present at the time of first MBL diagnosis.