Prognostic Impact Of Somatic NOTCH2 Mutation In Splenic Marginal Zone Lymphoma

New insights in the pathogenesis of the splenic marginal zone lymphoma (SMZL) has been recently enlightened by next generation sequencing technology discovering recurrent mutations in several genes implicated in major signalling pathways. In 2 recent reports (JEM 2012), mutations in NOTCH2, a gene encoding a protein required for marginal zone B-cell development, were identified in nearly 25% of the patients, with controversial impact on clinical outcome. The aim of our analysis was to analyse the incidence and the prognostic impact of somatic NOTCH2 mutations in a large cohort of patients with SMZL homogeneously treated.

A series of 105 consecutive SMZL patients requiring treatment and referred in 2 expert centers was analysed. Genomic DNA was extracted from frozen tumor samples of involved spleen or blood or bone marrow obtained at diagnosis. Tumor cell clonality was established by amplification of the rearranged IGH genes. Targeted sequencing of the NOTCH2 C-terminal coding exons 26, 27 and 34 was performed using Sanger sequencing and primers described by Kiel MJ et al (J.Exp.Med.209:9,2012). All mutations were verified in at least two independent PCR amplification and sequencing reactions. Log-rank tests were used to compare survival times -overall survival (OS) and progression-free survival (PFS)- between patients with mutated NOTCH2 and patient with wild-type NOTCH2. We controlled the effects of prognostic factors on outcome using multivariate Cox model analysis.

The median follow-up was 7 years. At diagnosis, median age was 63 years. Sex ratio was M/F 1:1.35. Nearly all patients presented with a disseminated disease and a good performance status. Forty-four percent of the patients had a high LDH level. A monoclonal component was detected in 31% of the patients. An immunological event such as haemolytic anemia, thrombocytopenia, neutropenia, coagulation disorder, and cryoglobulinemia, was observed in 27% of the patients. None of the patients was infected with hepatitis C virus. Patients were scored according to the age-adjusted International Prognostic Index (n=95), and to the IIL score system (n=76). Splenectomy was realized in 97% of the patients. Three patients were treated with R-Bendamusine without splenectomy. Adjuvant treatment after splenectomy was proposed for 24% of the patients, and included CHOP+/-R (n=16), HLX-VP16 (n=1), chlorambucil (n=4), and rituximab alone (n=1). Five and 10-year OS was estimated at 82% and 69%, respectively. Five and 10-year PFS was estimated at 61% and 46%, respectively. Age>60 was significantly associated to a shorter OS (p=0.0135).

We identified NOTCH2 mutations in 10 (10%) of the patients. The detected mutations occurred only within the exon 34 (TAD and PEST domains) and represented mostly truncating or insertional events leading to frameshift mutations (8 of the 10 cases) (also 1 nonsense and 1 missense mutations). Comparison of the clinical characteristics at diagnosis between patients with or without NOTCH2 mutations did not show any significant differences. Patients with NOTCH2 mutations were characterized by a significantly worse OS (at 5 years, 32% vs 87%, p<0.0001). Presence of NOTCH2 mutations was also significantly associated with a shorter PFS (at 5-years, 16% vs 66%; p=.0008), and with a shorter time to histological transformation (at 5 years, 26% vs 6%; p=0.0051). NOTCH2 mutational status did not influence the time to first treatment. Multivariate analysis showed an independent prognostic impact of NOTCH2 mutational status on OS (RR 4.7, p=0.02).

NOTCH2 mutation was identified in 10% of the SMZL patients in our series. Our data demonstrate also, as described, than patients with NOTCH2 mutations have a significant poorer prognosis than patients without NOTCH2 mutations, with a shorter PFS and a shorter OS. NOTCH2 mutational status seems to be an independent prognostic factor. This needs to be confirmed in prospective trials in the context of new therapeutics.

CA and GB equally contributed

Coiffier:Millennium Pharmaceuticals : Consultancy.