BackgroundDecitabine was evaluated for its efficacy and safety in Korean patients with myelodysplastic syndrome with IPSS score of 0.5 or over. Design and MethodsDecitabine 20 mg/m 2 /day was given intravenously over one hour for five consecutive days every four weeks. The primary end point was overall response rate. ResultsA total of 101 patients were analyzed. The International Prognostic Scoring System risk category was Intermediate-2/High in 47.5%. A median of 5 courses (range 1-18) were delivered. The overall response rate was 55.4% (13 complete responses, one partial response, 23 marrow complete responses, and 19 hematologic improvements). Forty-eight patients (47.5%) showed some hematologic improvement. With a median follow-up duration of 478 days (range 69-595), median overall survival was 17.7 months. Patients who showed hematologic improvement had significantly longer overall survival than those who did not (19.2 vs. 15.9 months, P=0.006 by landmark analysis at six months). The difference in overall survival was evident in the Intermediate-2/High risk group but not in the Intermediate-1 risk group. The progressionfree survival and acute myeloid leukemia-free survival were 61.9% and 77.9% at one year, respectively. Among 489 assessable treatment courses, there were 97 fever episodes requiring intravenous antimicrobials. ConclusionsDecitabine treatment was feasible and effective in Korean patients with myelodysplastic syndrome, and the overall survival was significantly longer in patients showing hematologic improvement. (ClinicalTrials.gov Identifier: NCT01041846)