The present invention provides for a method of treating cancer and/or reducing proliferation of cancer cells, the method comprising administering to a subject in need of such treatment a composition comprising a PIM kinase inhibitor that exhibits changes of mRNA splicing in combination with a compound that modulates/inhibits activity of an RNA splicing factor protein. Further, changes in splicing of mRNAs and phosphorylation of RNA splicing factors can be used as biomarkers for patient responsiveness to anti-PIM treatment and also suggest effective combinatorial therapies, including synergistic combination.