Morosini, Deborah

497 Background: As activating RAS mutations have been shown to predict lack of benefit from anti-EGFR therapies in advanced CRC, NCCN guidelines recommend testing for KRAS exon 2 and non-exon 2 mutations; however, these alterations are thought to explain only a subset of de novo resistance to targeted therapy. In a large set of CRC assayed with comprehensive genomic profiling (CGP) in the course of clinical care, we assessed the frequency of less common KRAS short insertions that may predict failure of anti-EGFR therapy. Methods: 4,422 CRC cases were assayed with CGP performed on hybridization-captured, adaptor ligation based libraries to a mean coverage depth of > 650X for at least 236 cancer-related genes plus 47 introns from 19 genes frequently rearranged in cancer. All classes of genomic alterations (GA) were identified, including base pair substitutions, insertions/deletions, copy number alterations, and rearrangements. Pertinent available prior molecular testing results and clinical history was reviewed for selected cases. Results: Out of 4,422 CRC cases analyzed, KRAS short variants were identified in 50.9% of cases. A majority of cases contained a KRAS alteration at either codon G12 (35.5%) or G13 (9.1%), while alterations at codons Q61 or A146 were identified in 2.2% and 3.1% of cases, respectively. KRAS insertions were identified in 8 ( < 0.5%) cases. All KRAS insertions identified fell within codons 9-13, and 6/8 cases harbored V9_G10 insertions. Out of 6 patients with prior KRAS testing results available, 5 (83%) were negative by previous testing. Conclusions: CGP identifies KRAS insertions within or adjacent to hotspot regions in CRC cases which have previously tested negative for KRAS mutations. Given the importance of KRAS alterations in predicting lack of response to anti-EGFR therapies in CRC, accurate detection of these alterations in the course of clinical care is essential for effective treatment. CGP offers the possibility of identifying KRAS insertions that may impact efficacy of anti-EGFR targeted therapy and should be considered when previous focused testing for KRAS mutations is negative.

Abstract Background: Previous failed trials of anti-EGFR therapy (TBCRC001) in breast cancer have not directly assessed EGFR amplification instead relying on pathway activation surrogates. Previous studies have examined EGFR amplification primarily retrospectively for research purposes without being part of a standard diagnostic evaluation. We evaluated 5,606 clincally advanced breast cases for which comprehensive genomic profiling was performed in the course of clinical care to identify EGFR altered mBC cases. Methods: DNA was extracted from 40 microns of FFPE sections from 5,605 mBC. Comprehensive genomic profiling (CGP) was performed using a hybrid-capture, adaptor ligation based next generation sequencing assay of up to 236 or 315 genes to a mean coverage depth of &gt;600X. The results were analyzed for base substitutions, short insertions and deletions, selected rearrangements, and copy number changes. Results: 155 (2.7%) of 5,605 mBC featured EGFR alterations. 126 (10.6%) featured EGFR amplification, and 27 (2.2%) featured ERBB2 subs/indels, with no cases harboring both amplification and another GA of EGFR. These patient (pts) had a median age of 55 years (range 30 to 78). For EGFR altered cases, specimens utilized for CGP included 59 (38%) from the patient's primary BC and 93 (60%) from metastatic sites including liver (14%), lymph node (14%), lung (8%), soft tissue (6%), skin (5%) and with information not available for 3 cases. 75 (48%) mBC were submitted as IDC, 69 (45%) as breast carcinoma NOS, 5 (3 %) as metaplastic BC, and 7 (5%) as other mBC. For the 126 EGFR amplified breast patients, quantitative estimation of EGFR copy number ranged from 6 to 380 copies, with a median of 12 copies. A patient with heavily pretreated case and whose TNBC harbored 32 copies of EGFR was begun on erlotinib and has experienced a 20 months ongoing complete response to erlotinib, and will be presented as will other outcomes and biomarker characterization of these cases. Conclusions: Given anecdotal evidence that mBC is responsive to anti-EGFR targeted therapies, prediction of benefit from such therapies may be linked to sensitive and specific detection of EGFR alteration in mBC cases. This study demonstrates a 2.7% EGFR alteration rate of mBC, with a striking median copy number of 12 for the subset of EGFR amplified cases. Given these findings along with anecdotal report of patient benefit, utilization of CGP in the course of clinical care or for clinical trials for mBC may help optimize treatement with targeted therapies for these patients including the direction of anti-EGFR monotherapy to EGFR altered patients. Citation Format: Ali SM, Wang K, Johnson A, Rodriguez AA, Elvin JA, Vergilio J-A, Suh JH, Chumsri S, Morosini D, Yelensky R, Lipson D, Chmielecki J, Miller VA, Ross JS, Chang J, Stephens PJ. EGFR genomic alterations in 5,605 cases of refractory and metastatic breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-03-02.