Genomic DNA from cell lines with defined mutations in p53 exons, DU145 (exon 6), SW480 (exons 8 and 9), DLD1 (exon 7) and BT483 (exon 7) was extracted from cell lines purchased from the American Type Culture Collection (ATCC), or purchased as purified DNA when available. Surgical colon and lung cancer tumor samples were obtained from the Massachusetts General Hospital Tumor Bank following Internal Review Board approval. DNA from the EGFR mutation-positive cell lines A549, HCC827, H1975 and LU011 and from formalin-fixedparaffin-embedded lung cancer samples were obtained from the Lowe Center for Thoracic Oncology, Dana Farber Cancer Institute following Internal Review Board approval. We isolated genomic DNA using DNeasy TM Tissue Kit (Qiagen).