The invention relates to histone deacetylase (HDAC) biomarkers in multiple myeloma. Specifically, the biomarkers are drug specific, histone deacetylase (HDAC) or HDAC6 biomarker RNAs for multiple myeloma. The invention also relates to a kit for determining the treatment efficiency of a HDAC6 inhibitor, and a kit for identifying a histone deacetylase 6 (HDAC6) inhibitor. The invention further relates to a method for monitoring treatment efficiency of an HDAC inhibitor in a subject.