Based on previous studies in which we observed elisidepsin treatment-induced HER3 downregulation [11], in addition to the fact that high expression of the HER3 receptor tyrosine kinase is prevalent in tumor cells, including cancers of the breast, ovary and prostate [35], [36], [37], [38], [39], [40], [41], [42], we correlated basal protein expression levels of HER3 with sensitivity to elisidepsin in a panel of tumor cell lines with variable expression of this receptor and found that downregulation of HER3 exerted a protective effect against elisidepsin cytotoxicity. This evidence concerns the gene ERBB3 and cancer.