Analyzed homogeneously treated cohort of CLL cases at multiple time points before and after therapy.

Performed WES in 30 sequential samples from 12 CLL cases.

All received PCR based chemoimmunotherapy as initial treatment.

Of these 12 cases, two had samples available both >6 months prior to enrollment and at treatment initiation, seven patients who experienced relapse had samples available at both treatment initiation and at and time of relapse, and three patients had samples >6 months prior to enrollment, at treatment initiation, and at relapse.

Overall, detected total of 219 nonsynonymous Single Nucleotide Variants (SNV) and indels (average 19, range 11-33).

Del13q (42%) identified as most prevalent copy number abnormality followed by trisomy 12 (33%), del11q and del17p (17% each).

Recurrent mutations identified in NOTCH1 (33%), DDX3X (25%), TP53, SF3B1 XPO1 and MED12 (17% each). Other tumor implicated genes such as CARD11, NOTCH2, NOTCH4, DIS3, TRAF2, NFKBID, CHK2 and RB1 found mutated in individual cases.

In all 12 cases we identified at least one relevant cytogenetic abnormalities (del11q32, del13q14, del17p13, trisomy 12) and/or a mutated driver gene.

By WES, identified multiple subclones in 58% of cases (7 of 12 cases), as compared to previously identified 33% (4 of 12 cases) y CGH/FISH.

In 5 chemotherapy naïve cases, no significant increase in genomic complexity detected with disease progression.

In contrast, 5 out of 10 cases with samples analyzed before CIT and at time of relapse had changes in clonal dynamics.

Interestingly another clone emerged after relapse that harbored an independent del11q22 and mutations affecting different aminoacids of SF3B1 (K700E) and DDX3X (pL21fs).

Strong selection of impairment in these genes during disease progression suggests key role of these pathways/genes in pathogenesis of this patient.

Studies provide additional insight into genomic landscape and clonal architecture in cohort of homogeneously treated CLL cases before and after therapy.

Stable clonal architecture seen in prior to treatment, whereas clonal evolution leading to increased tumor heterogeneity occurred after under selection selective pressure of therapy in relapsed cases.

Early identification of tumoral heterogeneity and underlying genetic abnormalities might provide better targets for therapy to decrease likelihood of relapse.