Based on these results, we designed a phase Ib clinical trial to evaluate the activity of ricolinostat plus nab-paclitaxel in metastatic BC patients. Expansion of our analysis to other tumor types identified multiple cohorts enriched in high HDAC6 score samples. These results suggest that the HDAC6 score may provide an effective, CLIA certified predictive biomarker of ricolinostat sensitivity in multiple human cancers.