The purpose of this study is to investigate the overall response rate (ORR) and safety when treating patients with myelodysplastic syndrome with decitabine. Decitabine is to be administered as long as there is evidence of clinical benefit.

This study is a prospective (the study follows a group of individuals over time), open label (all people involved know the identity of the intervention), multicenter, single arm (one group of patients receiving the same treatment), observational study to observe the response rate and safety of decitabine when treating patients with myelodysplastic syndrome with decitabine. Decitabine is to be administered as long as there is evidence of clinical benefit. It will be assessed if the treatment duration could be prolonged by appropriate toxicity management such as an active antibiotic prophylaxis or dose and schedule modification, and whether this leads to potentially increased clinical benefits such as higher response rate, longer time to Acute Myeloid Leukemia, and prolonged overall survival. For safety evaluation, adverse events and peripheral blood findings will be collected. The patient will receive decitabine intravenous injection 20mg/m2 once a day for 5 consecutive days every 4 weeks.

Inclusion Criteria:

• Patients diagnosed with (primary or secondary) Myelodysplastic Syndrome including Chronic Myelomonocytic Leukemia (CMML)
• Patients with an International Prognostic Scoring System >= Int-1
• Patients who were never treated with hypomethylating agent (azacitidine and decitabine)
• Female patients who are postmenopausal or received contraceptive operation or refrain from sexual relations. Women of childbearing potential should conduct an effective method of birth control (oral contraceptives, injections, intrauterine device, double barrier method, contraceptive patch and male partner's sterilization), in case of male patients who will not have a baby within 2 months after the completion of decitabine therapy
• Patients who signed an informed consent document indicating that they understand the purpose of and procedures required for the study and are willing to participate in the study.

Exclusion Criteria:

• Patients diagnosed with Acute Myelogenous Leukemia (AML, bone marrow stem cell counts exceeding 20%) or other progressive malignant diseases
• Patients with active infection of virus or bacteria
• Patients who used to be treated with azacitidine or decitabine
• Patients who are hypersensitive to excipients of decitabine
• Patients who are pregnant or breast-feeding.

Secondary or tertiary hospitals in South Korea