CLL-240 Frequency of IKZF3 L162R Mutation in B-Cell Lymphoproliferative Disorders.

A mutation of AIOLOS/IKZF3, a member of the IKAROS family transcription factors has been identified as a putative driver of chronic lymphocytic leukemia (CLL) through large-scale WES studies of CLL patients, with a frequency of ~3% CLLs. The mutation has been detected uniquely as a hotspot mutation (L162R), localized within the DNA binding domain, conferring a gain-of-function by altering DNA binding specificity and expression of IKZF3 target genes, resulting in overexpression of B-cell receptor (BCR) signaling genes. Apart from CLL, IKZF3 mutations are rarely described in other B-cell lymphomas. In this study, we aimed to evaluate the frequency of IKZF3 mutations in lymphoproliferative B-cell disorders. By reviewing the literature and reanalyzing the cBioPortal database, IKZF3 was reported to be mutated in 31 cases, including 16 CLL, 10 DLBCL, 1 MCL, 1 MW, and 3 FL. Interestingly, the p.L162R hotspot mutation identified in CLL occurred in 17/31 cases, suggesting a selection of this gain-of-function mutation and a common mechanism of lymphomagenesis. Targeted NGS sequencing of a 13-gene panel, including exon 5 of IKZF3, was used to analyze a French multicentric prospective cohort of 650 CLL patients. We confirmed the presence of the IKZF3-L162R mutation with a frequency of 2% (n=13/650) in CLL. We next designed a droplet digital PCR assay, allowing the detection of the IKZF3-L162R mutation with high sensitivity in a retrospective cohort of 48 patients harboring an MYD88 L265P mutation, including 2 DLBCL and 46 Waldenstrom's macroglobulinemia (WM) cases. Among the 48 patients tested, the mutation was detected in 3 patients with WM disease (3/46; 6.5%) with a variant allelic frequency (VAF) of 0.7%, 1%, and 3%. These patients were symptomatic with anti-MAG antibodies or organomegaly. Targeted NGS sequencing confirmed the presence of the IKZF3-L162R mutation in the samples with VAF >1%. Altogether, IKZF3-L162R mutation occurs in CLL but also in other B-cell neoplasms with similar frequencies, suggesting a common mechanism of lymphomagenesis related to the dysregulation of BCR-signaling genes. We are currently sequencing more samples, including marginal zone lymphoma, to better appreciate the distribution of this mutation among B-cell lymphomas.