To target cancer cells selectively, we developed the therapeutic peptide, R9-caPep, which contains the L126-Y133 octapeptide region of PCNA and demonstrated that this peptide selectively kills NB cells and is especially toxic to MYCN-amplified NB cell lines, demonstrating its potential utility in treating patients with high-risk MYCN-amplified tumors. The gene discussed is PCNA; the disease is cancer.