Genetic Response to Lenalidomide in the Circulating Progenitor Cell Compartment of MDS Cohort. Preliminary Results of the Multicenter German LE-MON-5 Study

LE-MON-5 is a multicenter German phase-II study to verify the safety of monotherapy with lenalidomide (LEN) in MDS patients (pts) with IPSS low or Int-1 and isolated del(5q). We report our cytogenetic results after a monitoring period of sixteen months since start of the trial.

For sequential and frequent survey of LEN-treated pts we applied FISH on enriched CD34+ stem cells from peripheral blood (CD34+ pb) every 2–3 months using a panel of 8 to 13 probes. Karyotyping and FISH on bone marrow aspirates was performed at initial screening and every six months. The median number of analyzed metaphases was 25 (4–30) and FISH analyzing was based on 200 interphase nuclei.

We have already screened 94 pts and could confirm isolated del(5q) in 76 (81%). Due to our cytogenetic results demonstrating additional changes in 18/94 (19%) pts, these were registered as screening failures and thus excluded from the study. Until now cytogenetic follow-up data for 40 pts is available. After a median follow-up of 9 months (2–16 months) we have observed a significant impact of LEN on the reduction of the clone size (p < 0.05) by FISH-monitoring. Based on cytogenetic remission, we have separated the cohort into three groups: Fast responders (14/40 (35%) pts) showed a very rapid cytogenetic response to therapy with >50% reduction of 5q- clone size within two months. In the second group, the slow responders, we observed >50% reduction of clone size in 9/40 (22.5%) after > two months. However, two pts showed an increase of 5q- clone after 12 and 13 months respectively after initial response in the sense of a relapse. In the third group, the non responders, (11/34 (27.5%)) we could not observe any cytogenetic response during the as yet limited observation period. In six cases (15%) we detected a reduction of the 5q- clone during follow-up, but the emergence of additional aberrations were also observed such as: 1. trisomy 8 in 6.7% of metaphases after 8 months and is reduced to 3.6% after 12 months, 2. trisomy 4 in 6.7% of metaphases after 6 months and is disappeared after 12 months, followed by emergence of trisomy 8 in 8% of interphase cells, 3. finally, two cases showed loss of Y-chromosome after 4 months in 6% and 19% of CD34+ pb cells, respectively. In CD34+ pb cells of another case, trisomy 8 was detectable after two months in 3.5% of cells. All these new secondary abnormalities occurred in cells with normal chromosomes 5 and were slightly above or below our laboratory thresholds (3 times standard variation). In only one case, a new abnormality emerged in the 5q- clone: In this case additional del(20q) occurred after 2 months in 46% of CD34+ pb cells. In this case no reduction of 5q- cells after 4 months of treatment was observed. However, FISH analysis after 6 months of treatment showed a 14% reduction for both aberrations. To date we could not identify any pts who acquired complex anomalies while treated with LEN.

FISH analysis of CD34+ pb cells allows a reliable frequent and relevant genetic monitoring of treatment response to LEN. Our results confirm the positive and rapid effects of LEN on clones with del(5q): Thus, already after 2 months, we could observe up to 90% reduction in the 5q- clone size in 35% of pts. In general, remission rates increased with duration of therapy. We suspect that trisomy 4, 8 and Y-loss are fluctuant “mini clones” without any clinical relevance. Inclusion of additional pts and prolonged observation period will help us to better evaluate the clinical response to LEN.

Off Label Use: lenalidomide for MDS del(5q) provided by Celgene for this clinical study. Germing:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Braulke:Celgene: Honoraria, Research Funding. Schanz:Celgene: Honoraria, Research Funding. Giagounidis:Celgene: Honoraria. Götze:Celgene: Honoraria. Haase:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.