Comparisons of overall survival (OS) in patients treated with azacitidine according to the numbers of chromosome abnormalities (CAs); CA <3, CA=3, and CA>3 (A) and OS according to the numbers of CAs combined with the presence or absence of a monosomal karyotype (MK) (B). OS in the group with CA<3 was significantly higher than the other 2 groups (OS, 14.5% in the CA>3 group, 27.9% in the CA=3 group, 37.8% in the CA<3 group; CA<3 vs. CA=3, P=0.001). OS in the CA>3 group was lower than the other 2 groups (CA>3 vs. CA=3, P=0.001) (A). According to the presence or absence of MK combined with the number of CAs, OS was highest in the non-MK group with CA<3 compared to the other 5 groups (OS, 23.3% vs. 50.6% in the CA<3 groups with/without MK, 33.3% vs. 24.4% in the CA=3 groups with/without MK, 11.1% vs. 17.2% in the CA>3 groups with/without MK, P <0.001) (B).