Background: Isolated del 20q is common in MDS, and considered of good prognosis in the IPSS, but no large series of MDS with del 20q have been reported.

Methods: We studied characteristics and outcome of 64 MDS patients (pts) with isolated del 20q diagnosed between 1990 and 2008 in 5 centers of the GFM. They were also compared with MDS without del 20q included in the GFM registry (containing 995 karyotyped MDS diagnosed since 2003).

Results: Median age of the 64 MDS with isolated del 20q was 72 (48–92), with 41 males and 23 females. They included 34 RA, 8 RARS, 16 RAEB, 4 CMML and 2 RAEB-T. Fifty two percent of them had less than 5% of marrow blasts, compared to 34% in the non del 20q pts included in the GFM registry (p=0.006). Despite a significantly higher proportion of low and int-1 IPSS risk (90% vs 78%, p=0.021) the isolated del 20q cohort had lower platelet count (mean 156 vs 212 G/l, p=0.014) and higher reticulocyte count (mean 84 vs 52 G/l, p=0.012) than non del 20 q pts included in the GFM. No significant difference was found for age, gender, FAB, ANC and Hb level between isolated del 20q and non del 20q pts. When the analysis was restricted to pts with less than 5% marrow blasts, the same differences were seen between isolated del 20q and non del 20q pts. On the other hand, 12 (19%) of the pts with isolated del 20q had Hb > 12g/dl and platelets < 100 G/L vs 80 of non del 20q patients (p=0.007). The 12 pts with isolated del 20q and plts <100G/L without anemia, were mostly men (9/12), with marrow blasts <5% in 83% (10/12), and all (100%) had ANC >1 G/l. None of those del 20q pts progressed to AML (compared to 17% of isolated del 20 q pts with Hb <12 g/dl and/or plts >100 G/l) and their median overall survival was 39 months vs 29 months, respectively (p=0.32). Median survival of MDS with isolated del 20q was 37 months and was significantly longer in pts with marrow blasts <5% (12 vs 60 months, p=0,0001), with low and int-1 IPSS score (39 vs 11 months, p=0.01) and with Hb >11 g/dl (53 vs 16 months, p=0.002). Survival could not be compared between isolated del 20q and non del 20q pts because of the short observation period of the GFM registry.

Conclusion: MDS with isolated del 20q are characterized by usual absence of excess of blasts lower platelets and less anemia than other MDS. About 20% of them present with isolated thrombocytopenia. Prognosis is favorable only in the absence of excess of blasts.

Disclosures: No relevant conflicts of interest to declare.

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