The invention relates to methods for using biomarkers to identify cancer patients that will or are likely to respond to treatment. Specifically, the invention relates to the use of one or more of three association studies of cancer types, gene mutations, or gene expression levels in order to identify cancer patients that will or are likely to respond to treatment with a histone deacetylase (HDAC) inhibitor, alone or in combination with another cancer treatment. The methods may, optionally, further include treating such patient with an HDAC inhibitor, alone or in combination with another cancer treatment.
