Clinical Impact of TP53 Mutations in Patients with MDS and Isolated Deletion 5(q) Treated with Lenalidomid: Results from the German Prospective Le-Mon-5 Trial

Introduction: MDS with isolated deletion 5(q) accounts for approximately 5% of all MDS cases. A recent retrospective analysis has found a cumulative progression rate of 18% after 5 years in patients with MDS deletion 5(q) without an increased medullary blast count[1]. Retrospective analyses have indicated that mutations in TP53 have an adverse impact on the clinical course of affected patients and their response to Len treatment. Here we report on the results of the German multi-center, prospective Le-Mon-5 trial that investigated the safety and efficacy of lenalidomide (Len) in patients with MDS and isolated deletion 5(q).

Methods: Le-Mon-5 is a trial of Len in patients with MDS with isolated 5q abnormality, a blast count of < 5% in the bone marrow, a platelet count > 50.000/µl and absolute neutrophil counts of > 500/µl in the peripheral blood. Patients were treated with the standard dose of 10 mg Len for 21 days q28 days. The primary endpoint was safety. Secondary endpoints included response according to IWG criteria (2000), time to response, duration of transfusion independency and incidence and time to AML-transformation, respectively. All patients gave written informed consent to the trial including additional molecular genetic analyses. Central cytologic, cytogenetic and histologic review was performed. Mutational analysis of TP53 was done by next generation sequencing (NGS). For generation of PCR amplicon libraries TP53 primer plate assays were used and technically validated within the IRON-II (Interlaboratory Robustness Of Next generation sequencing) study network. Amplicon sequencing of TP53 was performed on a Roche 454 GS Junior system. Mean coverage of sequenced exons was about 800-fold allowing an approximate detection sensitivity of 2% mutational burden.

Results: A total of 91 patients were enrolled into the trial. Of those, 71 patients (male, n=13) were analyzed for TP53 mutations. Median age was 71 years (range 40-88 years). TP53 mutations prior to treatment initiation with Len were found in 7 patients (10%). There was no difference between the TP53 mutated (TP53^mut) versus TP53 wildtype patients (TP53^WT) with regard to age, IPSS risk, hemoglobin levels, absolute neutrophil counts and platelet counts at baseline. Transfusion independence was achieved in a significantly lower proportion of patients in the TP53^mut group versus TP53^WT group (43% vs. 62%, p=0.036). Moreover, median survival was significantly shorter in the TP53^mut group as compared to TP53^WT group (533 days vs. not reached, p=0.0002). No difference was seen with regard to cytologic and cytogenetic response. Data on evolution into AML are currently being collected. Of 2 patients we had follow-up samples available. Both patients showed no difference with regard to the mutation frequency after a follow-up of 4-17 months on Len treatment (27% and 51%, respectively), although one of the patients achieved a complete cytogenetic response during Len treatment.

Conclusions: Using the NGS technique on a routine basis, we achieved high quality runs with a high mean coverage of analyzed exons of TP53. Presence of TP53 mutations adversely affected response to Len with regard to transfusion independence. Moreover, TP53^mut patients had a shorter overall survival as compared to TP53^WT patients underlining the prognostic relevance of TP53 mutations in this patient cohort. Therefore, mutation analysis of TP53 might guide treatment decisions in the future, e.g. consideration of combination regimens. Since the TP53 clone obviously prevails during Len treatment, careful monitoring for signs of transformation should be performed.