Fludarabine, cyclophosphamide, and rituximab (FCR) is first-line treatment of medically fit chronic lymphocytic leukemia (CLL) patients; however, despite good response rates, many patients eventually relapse. Although recent high-throughput studies have identified novel recurrent genetic lesions in adverse prognostic CLL, the mechanisms leading to relapse after FCR therapy are not completely understood. To gain insight into this issue, we performed whole-exome sequencing of sequential samples from 41 CLL patients who were uniformly treated with FCR but relapsed after a median of 2 years. In addition to mutations with known adverse-prognostic impact (TP53, NOTCH1, ATM, SF3B1, NFKBIE, and BIRC3), a large proportion of cases (19.5%) harbored mutations in RPS15, a gene encoding a component of the 40S ribosomal subunit. Extended screening, totaling 1119 patients, supported a role for RPS15 mutations in aggressive CLL, with one-third of RPS15-mutant cases also carrying TP53 aberrations. In most cases, selection of dominant, relapse-specific subclones was observed over time. However, RPS15 mutations were clonal before treatment and remained stable at relapse. Notably, all RPS15 mutations represented somatic missense variants and resided within a 7 amino-acid, evolutionarily conserved region. We confirmed the recently postulated direct interaction between RPS15 and MDM2/MDMX and transient expression of mutant RPS15 revealed defective regulation of endogenous p53 compared with wild-type RPS15. In summary, we provide novel insights into the heterogeneous genetic landscape of CLL relapsing after FCR treatment and highlight a novel mechanism underlying clinical aggressiveness involving a mutated ribosomal protein, potentially representing an early genetic lesion in CLL pathobiology.

1st Department of Propaedeutic Medicine School of Medicine University of Athens Athens Greece;

2nd Medical Department University Hospital Schleswig Holstein Campus Kiel Kiel Germany; and

Cancer Sciences Faculty of Medicine University of Southampton Southampton United Kingdom;

Central European Institute of Technology Masaryk University and University Hospital Brno Brno Czech Republic;

Department of Haematology Royal Bournemouth Hospital Bournemouth United Kingdom;

Department of Immunology Genetics and Pathology Science for Life Laboratory Uppsala University Uppsala Sweden;

Department of Immunology Genetics and Pathology Science for Life Laboratory Uppsala University Uppsala Sweden; Institute of Applied Biosciences Center for Research and Technology Hellas Thessaloniki Greece; Hematology Department and Hematopoietic Cell Transplantation Unit G Papanicolaou Hospital Thessaloniki Greece;

Department of Immunology Laboratory for Medical Immunology Erasmus MC University Medical Center Rotterdam The Netherlands;

Department of Laboratory Medicine Stem Cell Center Lund University Lund Sweden;

Department of Medical Sciences Section of Hematology Uppsala University Uppsala Sweden;

Department of Medicine Hematology and Clinical Immunology Branch Padua University School of Medicine Padua Italy

Department of Medicine Solna Clinical Epidemiology Unit Karolinska Institutet Stockholm Sweden;

Division of Hematology Department of Translational Medicine Amedeo Avogadro University of Eastern Piedmont Novara Italy;

Hematology Department and Hematopoietic Cell Transplantation Unit G Papanicolaou Hospital Thessaloniki Greece;

Hematology Department General Hospital of Nikea Piraeus Greece;

Institute of Applied Biosciences Center for Research and Technology Hellas Thessaloniki Greece;

Karches Center for Chronic Lymphocytic Leukemia Research The Feinstein Institute for Medical Research Manhasset New York;

Laboratory of Hematology and Universite Pierre et Marie Curie Hopital Pitie Salpetriere Paris France;

Oxford National Institutes of Health Research Biomedical Research Centre University of Oxford Oxford United Kingdom;

Università Vita Salute San Raffaele and Division of Experimental Oncology and Department of Onco Hematology Istituto di Ricovero e Cura a Carattere Scientifico San Raffaele Scientific Institute Milan Italy;

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Blood. 2016 Feb 25;127(8):958-9. doi: 10.1182/blood-2015-12-688994. PubMed

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