Persistent polyclonal binucleated B-cell lymphocytosis and MECOM gene amplification.

Background: Persistent Polyclonal Binucleated B-cell Lymphocytosis (PPBL) is characterized by a chronic polyclonal B-cell lymphocytosis with binucleated lymphocytes and a polyclonal increase in serum immunoglobulin-M. Cytogenetic is characterized by the presence of a supernumerary isochromosome +i(3)(q10), premature chromosome condensation and chromosomal instability. Outcome of PPBL patients is mostly benign, but subsequent malignancies could occur. The aim of our study is to provide an update of clinical and cytogenetic characteristics of our large cohort of PPBL patients, to describe subsequent malignancies occurring during the follow-up, and to investigate the role of the long arm of chromosome 3 in PPBL.

Results: We analyzed clinical, biological and cytogenetic characteristics (conventional cytogenetic analysis and fluorescent in situ hybridization) of 150 patients diagnosed with PPBL. We performed high-resolution SNP arrays in 10 PPBL patients, comparing CD19(+) versus CD19(-) lymphoid cells. We describe the cytogenetic characteristics in 150 PPBL patients consisting in the presence of supernumerary isochromosome +i(3)(q10) (59%) and chromosomal instability (55%). In CD19(+) B-cells, we observed recurrent copy number aberrations of 143 genes with 129 gains (90%) on 3q and a common minimal amplified genomic region in the MECOM gene. After a median follow-up of 60 months, we observed the occurrence of 12 subsequent malignancies (12%), 6 solid tumors and 6 Non-Hodgkin's Lymphomas, and 6 monoclonal gammopathies of undetermined significance (MGUS), requiring a long-term clinical follow-up.

Conclusions: Our clinical and cytogenetic observations lead us to hypothesize that isochromosome 3q, especially MECOM abnormality, could play a key role in PPBL.