In CLL with Normal Karyotype By Conventional and Genomic Array Karyotyping the Prognostic Impact of an Unmutated IGHV Status Is Stronger Than the Impact of Gene Mutations

Background: In 15-20% of CLL cases no aberrations are detected by chromosome banding analysis (CBA) and FISH due to limited resolution, lack of evaluable metaphases or presence of aberrations in loci not covered by standard-panel FISH probes. As reported in our previous study (Haferlach C. et al., ASH 2015, abs ID#79545), genomic arrays (GA) detected abnormalities in almost 20% of cases classified as normal by CBA and FISH and these showed an impact on time to first treatment (TTT) (Vetro C. et al., EHA 2016, abs ID# E1069).

The CLL subgroup without abnormalities in CBA, FISH, and GA has not been characterised in detail, so far.

Aims: 1) to describe CLL without abnormalities by CBA/FISH/GA by evaluating an extended gene panel, the IGHV mutation status and the B-cell receptor (BCR) stereotypy; 2) to determine prognostic impact of these factors.

Patients and Methods: CLL diagnosis was based on cytomorphology and immunophenotyping according to standard guidelines. From a cohort of 1190 patients at diagnosis, 133 (11%) were selected based on normal karyotype by CBA, no abnormalities by interphase FISH with probes for 17p13 (TP53), 13q14 (D13S25, D13S319, DLEU), 11q22 (ATM), centromeric region of chromosome 12 and t(11;14)(q13;q32) (IGH-CCND1) and no abnormalities by GA (SurePrint G3 ISCA CGH+SNP Microarray, Agilent, Waldbronn, Germany).

IGHV mutation status and BCR stereotypy were determined according to Agathangelidis et al., Blood 2012, and DNA sequencing was performed for the following genes: ATM; SF3B1; TP53; KLHL6; KRAS; MYD88; NOTCH1; NRAS; POT1; FBXW7; HIST1H1E; XPO1; ITPKB; MAPK1; BIRC3; BRAF; DDX3X; EGR2; RIPK1; RPS15; CND2.

Results: Median age was 66 years (range: 33-83). Median follow-up was 5.6 years, 33 patients (25%) received treatment since genetic analyses. 10-year overall survival (OS) was 76% and median TTT was 9.2 years. Mutations were observed in 53 patients (40%): SF3B1 (n=17; 13%); NOTCH1 (n=10; 8%); KLHL6 (n=6; 5%); TP53 (n=6; 5%); ATM (n=5; 4%); XPO1 (n=4; 3%); FBXW7 (n=3; 2%); MYD88 (n=3; 2%); DDX3X (n=2; 2%); POT1 (n=2; 1.5%); ITPKB (n=1; 1%); KRAS (n=1; 1%); NRAS (n=1; 1%); and no mutation in RPS15, CCND2, MAPK1, EGR2, BRAF, HIST1H1E, RIPK1, BIRC3. 6 patients had 2 simultaneous gene mutations and 1 patient had 3 (i.e. NOTCH1, ATM and TP53).

A mutated IGHV status (IGHV-M) was present in 100 patients (75%) and an unmutated IGHV status (IGHV-U) in 33 patients (25%). IGHV-U was related to both the occurrence of any gene mutation (p<0.001) and the number of gene mutations (p=0.001). NOTCH1 was mutated in 7 out of the 33 IGHV-U patients (21%), but only in 3 out of 99 IGHV-M patients (3%) (p=0.001). XPO1 mutation occurred in 4 IGHV-U patients (12%) and none out of IGHV-M (p<0.001). Two IGHV-U patients showed POT1 mutation (6%), but no IGHV-M case (p=0.014). 9 patients out of 133 (7%) showed BCR-stereotypy. 2 were in cluster CLL#1 (both showing NOTCH1 mutation), 2 in cluster CLL#2 (both of them with SF3B1 mutation), 2 in CLL#4, 1 in CLL#8 (showing NOTCH1 and XPO1 mutations), 1 in CLL#201 (with KLHL6 mutation) and 1 in CLL#202 (with mutations in ATM, TP53 and NOTCH1 genes).

In Kaplan-Meier analysis, IGHV-M patients did not reach a median TTT, while IGHV-U had a median of 5.1 years (p<0.001). Stereotypy rate was too low for reliable statistics. At univariate analysis, TTT was only influenced by: IGHV-U (relative risk (RR): 3.9, p<0.001), TP53 mutation (RR: 3.7, p=0.03), % CLL cells (RR: 1.2 per 10% increase, p=0.013), and number of mutations (RR: 1.8 per each mutation, p=0.031). Multivariate Cox regression analysis showed an independent role for IGHV-U status (RR: 3.3, p=0.002) and % CLL cells (RR: 1.2 per 10% increase, p=0.038)

Only age showed an impact on OS (RR: 1.2 per decade, p<0.001).

Conclusions: 1. The CLL subset without any genomic event by CBA/FISH/genomic array is characterized by very low frequency of IGHV-U status; 2. IGHV-U subgroup showed higher gene mutation rate compared to IGHV-M subgroup, in particular higher NOTCH1, XPO1 and POT1 mutation rate; 3. BCR stereotypy is less frequent than in CLL in general. 4. IGHV-U, as well as the higher disease burden (i.e. % CLL cells), has an independent negative impact on TTT. 5. Requirement for treatment is low and prognosis very favorable in CLL without any genomic event by CBA/FISH/genomic array and a mutated IGHV status.