Colorectal cancer (CRC) is the third most common cancer world-wide with 1.2 million patients diagnosed yearly. In late stage CRC, the most commonly used targeted therapies are monoclonal antibodies cetuximab and panitumumab, which inactivate EGFR1. Recent studies have identified alterations in KRAS2–4 and other genes5–13 as likely mechanisms of primary and secondary resistance to anti-EGFR antibody therapy. Despite these efforts, additional mechanisms of resistance to EGFR blockade are thought to be present in CRC and little is known about determinants of sensitivity to this therapy. To examine the effect of somatic genetic changes in CRC on response to anti-EGFR antibody therapy, we performed complete exome sequence and copy number analyses of 129 patient-derived tumorgrafts and targeted genomic analyses of 55 patient tumors, all of which were KRAS wild-type. We analyzed the response of tumors to anti-EGFR antibody blockade in tumorgraft models or in clinical settings. In addition to previously identified genes, we detected mutations in ERBB2, EGFR, FGFR1, PDGFRA, and MAP2K1 as potential mechanisms of primary resistance to this therapy. Novel alterations in the ectodomain of EGFR were identified in patients with acquired resistance to EGFR blockade. Amplifications and sequence changes in the tyrosine kinase receptor adaptor gene IRS2 were identified in tumors with increased sensitivity to anti-EGFR therapy. Therapeutic resistance to EGFR blockade could be overcome in tumorgraft models through combinatorial therapies targeting actionable genes. These analyses provide a systematic approach to evaluate response to targeted therapies in human cancer, highlight new mechanisms of responsiveness to anti-EGFR therapies, and provide new avenues for intervention in the management of CRC.

Massively parallel sequencing approaches are beginning to be used clinically to characterize individual patient tumors and to select therapies based on the identified mutations. A major question in these analyses is the extent to which these methods identify clinically actionable alterations and whether the examination of the tumor tissue alone is sufficient or whether matched normal DNA should also be analyzed to accurately identify tumor-specific (somatic) alterations. To address these issues, we comprehensively evaluated 815 tumor-normal paired samples from patients of 15 tumor types. We identified genomic alterations using next-generation sequencing of whole exomes or 111 targeted genes that were validated with sensitivities >95% and >99%, respectively, and specificities >99.99%. These analyses revealed an average of 140 and 4.3 somatic mutations per exome and targeted analysis, respectively. More than 75% of cases had somatic alterations in genes associated with known therapies or current clinical trials. Analyses of matched normal DNA identified germline alterations in cancer-predisposing genes in 3% of patients with apparently sporadic cancers. In contrast, a tumor-only sequencing approach could not definitively identify germline changes in cancer-predisposing genes and led to additional false-positive findings comprising 31% and 65% of alterations identified in targeted and exome analyses, respectively, including in potentially actionable genes. These data suggest that matched tumor-normal sequencing analyses are essential for precise identification and interpretation of somatic and germline alterations and have important implications for the diagnostic and therapeutic management of cancer patients.

Pancreatic adenocarcinoma has the worst overall mortality of any solid tumor, with only 6% of patients surviving after 5 years. To evaluate the clinical implications of genomic alterations in this low cellularity tumor type, we deeply sequenced the genomes of 134 enriched pancreatic adenocarcinomas from patients who underwent potentially curative resections. Given the low neoplastic cellularity of pancreatic cancers, we enriched for neoplastic cells either by macrodissection of primary tumors or by flow-sorting of tumor nuclei, and performed deep sequencing (high coverage) of these enriched samples using next-generation sequencing approaches. We obtained a total of >1Tb of sequence data, resulting in an average coverage within the target regions of >200-fold for each tumor analyzed by whole-exome sequencing and >750-fold for each tumor analyzed by targeted cancer gene sequencing. These approaches allowed us to identify sequence changes, including single base and small insertion or deletion mutations, as well as copy number alterations in >20,000 genes in the whole-exome analyses and in 116 specific genes in the targeted analyses. These analyses revealed that somatic mutation of chromatin remodeling genes were associated with improved progression-free and overall survival. Alterations in genes with potential clinical utility were observed in a majority of cases and included alterations of AKT1, AKT2, BRCA2, ERBB2, KIT, and PIK3CA. Non-invasive liquid biopsy analyses were performed before and after surgery to evaluate the presence of circulating tumor DNA in the plasma of 83 patients. Through these approaches, we were able to diagnose early stage pancreatic tumors in the majority of patients and to detect the presence of circulating tumor DNA prior to clinical relapse. These observations provide genetic markers of clinical outcome in pancreatic cancer and suggest new avenues for personalized therapy. Citation Format: Mark Sausen, Jillian Phallen, Vilmos Adleff, Siân Jones, Rebecca J. Leary, Karli Lytle, Sonya Parpart-Li, Derek Murphy, Michael T. Barrett, David C. Linehan, Anirban Maitra, Ralph Hruban, Daniel D. Von Hoff, Julia S. Johansen, Luis A. Diaz, Jeffrey A. Drebin, Victor E. Velculescu. Identification of clinically actionable genomic alterations in the tumor and circulation of pancreatic cancer patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 619. doi:10.1158/1538-7445.AM2015-619

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