Provided herein are methods for treating a subject having chronic myelomonocytic leukemia (CMML), the method comprising: (a) identifying a RAS pathway mutation in tumor cells of the subject, wherein the RAS pathway mutation is a NRAS, KRAS, and/or CBL mutation; and (b) administering to the subject identified in step (a) a therapeutically effective amount of an anti-hGM-CSF antibody. The subject may have a RAS pathway mutation or a RAS pathway mutation and at least one TET2 mutation identified in the tumor cells. The methods further comprise administering a therapeutically effective amount of a hypomethylating agent. Also provided herein are methods for treating a subject having chronic myelomonocytic leukemia (CMML), the method comprising: (a) identifying a RAS pathway mutation in tumor cells of the subject, wherein the RAS pathway mutation is a NRAS, KRAS, and/or CBL mutation; and (b) administering to the subject identified in step (a) a therapeutically effective amount of an anti-hGM-CSF antibody lenzilumab and a therapeutically effective amount of a hypomethylating agent. The subject may have a RAS pathway mutation or a RAS pathway mutation and at least one TET2 mutation identified in the tumor cells. A therapeutically effective amount of a hypomethylating agent is further administered according to the provided methods.