A 60-year-old woman with squamous cell carcinoma in the right lung was successfully treated with four cycles of combination chemotherapy after surgery, and complete remission was achieved. However, the patient developed myelodysplastic syndrome (MDS) RAEB-2 with myelofibrosis after remission, possibly because of chemotherapy or DNA methylation. The patient responded well to dacitabine (Dacogen), suggesting that DNA hypomethylation agents can be a promising therapy to retard the progression of a second tumor or carcinoma. A, 60-year-old woman with squamous cell carcinoma in the right lung was successfully treated with four cycles of combination chemotherapy after surgery, and complete remission was achieved. However, the patient developed myelodysplastic syndrome (MDS) RAEB-2 with myelofibrosis after remission , because because of chemotherapy or DNA methylation. The patient responded well to dacitabine (Dacogen), suggesting that DNA hypomethylation agents can be promising drugs to retard the progression of a second tumor or carcinoma.