Monitoring By Chromosome Banding Analysis (CBA) and FISH Of Circulating CD34+ Cells In Low-Risk MDS Patients Treated In The Le-Mon-5 Study With Lenalidomide Monotherapy Reveals 82% Cytogenetic Responders With Different Response – , Evolutionary -, and Remission Patterns and No Increased Karyotype Evolution (KE)

Besides a more reliable and frequent measurement of cytogenetic response, it was our aim to find out whether lenalidomide treatment in patients with IPSS low- or intermediate I-risk MDS can foster karyotype evolution (KE) and thus increase the risk of leukemic transformation. Thus, it is an important goal of the Le-Mon-5 study to examine the cytogenetic course under treatment with lenalidomide. In this study, only lower risk MDS patients with an isolated del(5q) are included.

We performed a rigid initial pretreatment screening of bone marrow (bm) aspirates by chromosome banding (CBA) as well as FISH-analysis to ensure an isolated del(5q). For initial screening as well as frequent cytogenetic follow-up every two to three months (FISH analysis of immunomagnetically enriched CD34+ peripheral blood cells (PBC) = CD34+ pb FISH), we used panels of 8 to 13 FISH probes covering the most common aberrations in MDS (Braulke et al. Leuk Res, 2010, 2013). Using this method we intended a reliable surveillance of cytogenetic changes occurring during therapy. Complete cytogenetic remission (CCyR) was defined as: no metaphases with del(5q) and abnormal FISH result below the laboratory threshold (5% EGR1-loss in CD34+ PBC) and partial cytogenetic remission (PCyR) was defined as: >50% reduction of clone size, also including cases with a CCyR at only one time point and those with either only CBA-CCyR or FISH-CCyR.

From the initially screened 145 MDS patients, 84 could be included in the study according to the study inclusion criteria. Currently, follow-up data (at least 2 different time points) are available for 67 patients. An ongoing (>1 time point) CCyR was observed in 22 (33%) patients after a median follow-up of 18 (6-33) months. Thirty-three patients (49%) had a PCyR. Considering only CD34+ pb FISH results 31 (46%) patients showed a complete molecular-cytogenetic remission.

A cytogenetic response was observed after a median of 6 (2-12) months after initiation of therapy for a median duration of 10 (2-25) months. In twelve patients (18%) the size of the del(5q) clone did not change. The median del(5q)-clone size at start of therapy was 60% in responders. After 10 cycles maximum clone size reduction was achieved (n=26) (median: 2.6%; range: 0% - 33.6%), after 24 months of observation clone size in responders (n=22) still was reduced to a median of 10.8% (range: 0.5% -76%) (Figure 1).

Figure 1

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Median and standard deviation of del(5q) clone sizes during treatment with lenalidomide

Figure 1

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Median and standard deviation of del(5q) clone sizes during treatment with lenalidomide

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In 10 of 67 patients (15%) a KE occurred in the del(5q) clone after a median time of 18 months (6-42). This is not increased compared to the rate of spontaneous KE (13%) in a representative MDS cohort (n=729) studied recently by our group by banding analysis (Cevik et al. DGHO 2013, accepted for oral presentation). Remarkably, in one patient a KE with loss of a p53 allele and a 20q- deletion resolved after the 8^th cycle of lenalidomide and after the 10^th cycle a complete cytogenetic remission was achieved (Figure 2). In two additional cases, the del(5q) clone was completely eliminated, however a new cell clone with independent abnormalities (t(3;3)(q21;q26), second case: inv(11)(p15q23)del(11)(q13q22)) emerged under lenalidomide. There is a growing body of evidence that these clones were preexistent initially but below the cytogenetic detection level and were possibly suppressed by the del(5q) clone until its cytogenetic remission.

Figure 2

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Cytogenetic course in a patient with transient KE

Figure 2

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Cytogenetic course in a patient with transient KE

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Our interim results show that:

• A cytogenetic response to lenalidomide can be achieved in >80% of pts. with isolated del(5q) and lower-risk MDS

• CBA can be complemented reasonable by CD34+ pB FISH, which allows a reliable monitoring of response and KE

• Cytogenetic response to lenalidomide is durable (median 10 months as yet)

• KE is not increased in this patient group under treatment with lenalidomide

• In one case with KE and acquisition of additional p53 allelic loss and 20q-deletion continuation of lenalidomide finally lead to a CCyR

Platzbecker:Celgene: Honoraria. Nolte:Celgene: Honoraria, Research Funding. Giagounidis:Celgene: Honoraria. Götze:Celgene Corp: Honoraria. Schlenk:Celgene: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Chugai: Research Funding; Amgen: Research Funding; Novartis: Research Funding; Ambit: Honoraria. Bug:Celgene: Honoraria, Research Funding. Germing:Celgene: Honoraria. Haase:Celgene: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding.