Gene Mutations and Treatment Outcome in Chronic Lymphocytic Leukemia: Results From the CLL8 Trial

Abstract 433

Novel gene mutations have been found in CLL by next generation sequencing including mutations of NOTCH1 and SF3B1 in 5–20% of cases. In initial studies, both have been associated with advanced disease and poor outcome.

We assessed the incidence and impact of gene mutations in the CLL8 trial (1^st line FC vs. FCR, n=817). TP53 (exons 2–11) was analyzed by a re-sequencing chip (Amplichip, Roche Molecular Systems) with confirmatory Sanger sequencing. NOTCH1 was analyzed by Sanger sequencing exon 34, chr9:139,390,619–139,391,290 (PEST domain). SF3B1 (exons 13–16) was analyzed by DHPLC (WAVE® 3500HT, Transgenomic Inc.) with subsequent Sanger sequencing. Baseline samples were available for analysis of genetic markers in 619 (75.8%) to 645 (78.9%) patients. All markers were available for 573 (70.1%) patients and this cohort was representative of the full trial population.

Mutations (^mut) were found in TP53, NOTCH1, and SF3B1 in 11.5%, 10.0%, and 18.4%, respectively. At least one mutation was identified in 35.2% patients, while 30.6% had one, 4.4% had two and 0.2% had three mutations. Concurrent NOTCH1^mut and SF3B1^mut were found in only 0.5% patients. TP53^mut was observed in 16.7% of NOTCH1^mut cases (p=.528) and in 14.5% of SF3B1^mut patients (p=.472).

Regarding baseline characteristics, there were significant associations of TP53^mut with CIRS>1, unmutated IGHV and 17p-; of NOTCH1^mut with Binet A/B, no B-symptoms, unmutated IGHV, and 17p-; and of SF3B1^mut with TK>10, and no +12.

Regarding response to therapy, TP53^mut was significantly associated with refractory disease in both arms (FCR: 25.0% vs. 1.8%, p<.001, FC: 48.4% vs. 7.8%, p<.001,); while NOTCH1^mut showed only a trend in the FCR arm (FCR: 10.9% vs. 3.4%, p=.109, FC: 11.9% vs. 12.9%, p=.775); and SF3B1^mut did not impact response to therapy (FCR: 3.6% vs. 3.7%, p=1.00, FC: 12.3% vs. 10.9%, p=1.00).

At extended follow-up (median 69.97 months), FCR resulted into significantly improved PFS (HR 0.586, p<.001) and OS (HR 0.678, p=.001). TP53^mut was associated in both treatment arms with significantly decreased PFS (FC: HR 4.295, p<.001; FCR: HR 3.173 p<.001) and OS (FC: HR 4.642 p<.001; FCR: HR 4.447, p<.001). In contrast, NOTCH1^mut was only in the FCR arm associated with significantly decreased PFS (FC: HR 0.931, p=.741; FCR: HR 1.718, p=.013) and a trend to inferior OS (FC: HR 0.854, p=.605; FCR: HR 1.610, p=.112). SF3B1^mut was associated in both treatment arms with significantly decreased PFS (FC: HR 1.520, p=.009; FCR: HR 1.463, p=.033) and a trend to inferior OS (FC: HR 1.338, p=.178; FCR: HR 1.305, p=.301).

To evaluate the independent prognostic impact, we performed multivariable analyses by Cox regression for PFS and OS including the following variables: treatment, age, sex, stage, ECOG status, B-symptoms, WBC, TK, β2-MG, 11q-, +12, 13q-, 17p-, IGHV, TP53, NOTCH1 and SF3B1. Regarding PFS, the following independent prognostic factors were identified: FCR (HR 0.510, p<.001), TK>10 (HR 1.367, p=.019), IGHV<98% (HR 1.727, p<.001), 11q- (HR 1.536, p<.001), 17p- (HR 2.949 p<.001), TP53^mut (HR 2.113 p<.001), and SF3B1^mut (HR 1.348, p=.024). Regarding OS, the following independent prognostic factors were identified: FCR (HR 0.701, p=.049), ECOG>0 (HR 2.202, p<.001), TK>10 (HR 2.707, p<.001), IGHV<98% (HR 1.547, p=.055), 17p- (HR 3.546 p<.001) and TP53^mut (HR 3.032 p<.001).

To identify a predictive impact of gene mutations for a specific treatment effect by the addition of rituximab, we performed multivariable analyses including the treatment arms, the gene mutations and the interaction of both. Regarding PFS, FCR (HR 0.544, p<.001), TP53^mut (HR 3.607, p<.001), SF3B1^mut (HR 1.355, p=.012) and NOTCH1^mut interaction with FCR (HR 1.652, p=.022) were identified as independent factors. Regarding OS, FCR (HR 0.654, p=.002) and TP53^mut (HR 4.470, p<.001) were identified as independent factors while NOTCH1^mut interaction with FCR (HR 1.331, p=.344) showed a trend. The interaction between NOTCH1^mut and FCR treatment is illustrated in univariate PFS analysis, in which the addition of rituximab led to a benefit only among patients without NOTCH1^mut (Figure).

In conclusion, gene mutations show independent prognostic value for PFS (TP53, SF3B1) and OS (TP53) in patients receiving 1^st line FC and FCR treatment. Of note, NOTCH1^mut appears to identify a subset of CLL patients that does not benefit from the addition of rituximab to FC.

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