Resistance to targeted therapies is a major problem in cancer treatment. The epidermal growth factor receptor (EGFR) antibody drugs are effective in a subset of colorectal cancers, but the molecular mechanisms of resistance are understood poorly. Genes involved in epigenetic regulation are frequently deregulated in cancer, raising the possibility that such genes also contribute to drug resistance. Using a focused RNA interference library for genes involved in epigenetic regulation, we identify sirtuin2 (SIRT2), an NAD(+)-dependent deacetylase, as a modulator of the response to EGFR inhibitors in colon and lung cancer. SIRT2 loss also conferred resistance to BRAF and MEK inhibitors in BRAF mutant melanoma and KRAS mutant colon cancers, respectively. These results warrant further investigation into the potential role of SIRT2 in resistance to drugs that act in the receptor tyrosine kinase-RAS-RAF-MEK-ERK signaling pathway.