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Purpose:We assessed plasma circulating tumor DNA (ctDNA) level as a prognostic marker for progression-free survival (PFS) following first-line metastatic colorectal cancer (mCRC) therapy.Experimental Design:The Sequencing Triplet With Avastin and Maintenance (STEAM) was a randomized, phase II trial investigating efficacy of bevacizumab (BEV) plus 5-fluorouracil/leucovorin/oxaliplatin (FOLFOX) and 5-fluorouracil/leucovorin/irinotecan (FOLFIRI), administered concurrently or sequentially, versus FOLFOX-BEV in first-line mCRC. Evaluation of biomarkers associated with treatment outcomes was an exploratory endpoint. Patients in the biomarker-evaluable population (BEP) had 1 tissue sample, 1 pre-induction plasma sample, and 1 post-induction plasma sample collected ≤60 days of induction from last drug date.Results:Among the 280 patients enrolled in STEAM, 183 had sequenced and evaluable tumor tissue, 118 had matched pre-induction plasma, and 54 (BEP) had ctDNA-evaluable sequencing data for pre- and post-induction plasma. The most common somatic variants in tumor tissue and pre-induction plasma were TP53, APC, and KRAS. Patients with lower-than-median versus higher-than-median post-induction mean allele fraction (mAF) levels had longer median PFS (17.7 vs. 7.5 months, HR, 0.33; 95% confidence interval, 0.17–0.63). Higher levels of post-induction mAF and post-induction mean mutant molecules per milliliter (mMMPM), and changes in ctDNA (stratified by a 10-fold or 100-fold reduction in mAF between pre- and post-induction plasma), were associated with shorter PFS. Post-induction mAF and mMMPM generally correlated with each other (ρ = 0.987, P < 0.0001).Conclusions:ctDNA quantification in post-induction plasma may serve as a prognostic biomarker for mCRC post-treatment outcomes.

Monitoring treatment efficacy early during therapy could enable a change in treatment to improve patient outcomes. We report an early assessment of response to treatment in advanced NSCLC using a plasma-only strategy to measure changes in ctDNA levels after one cycle of chemotherapy. Plasma samples were collected from 92 patients with Stage IIIB-IV NSCLC treated with first-line chemo- or chemoradiation therapies in an observational, prospective study. Retrospective ctDNA analysis was performed using next-generation sequencing with a targeted 198-kb panel designed for lung cancer surveillance and monitoring. We assessed whether changes in ctDNA levels after one or two cycles of treatment were associated with clinical outcomes. Subjects with ≤50% decrease in ctDNA level after one cycle of chemotherapy had a lower 6-month progression-free survival rate (33% vs. 58%, HR 2.3, 95% CI 1.2 to 4.2, log-rank p = 0.009) and a lower 12-month overall survival rate (25% vs. 70%, HR 4.3, 95% CI 2.2 to 9.7, log-rank p < 0.001). Subjects with ≤50% decrease in ctDNA level after two cycles of chemotherapy also had shorter survival. Using non-invasive liquid biopsies to measure early changes in ctDNA levels in response to chemotherapy may help identify non-responders before standard-of-care imaging in advanced NSCLC.

Purpose:We assessed plasma circulating tumor DNA (ctDNA) level as a prognostic marker for progression-free survival (PFS) following first-line metastatic colorectal cancer (mCRC) therapy.Experimental Design:The Sequencing Triplet With Avastin and Maintenance (STEAM) was a randomized, phase II trial investigating efficacy of bevacizumab (BEV) plus 5-fluorouracil/leucovorin/oxaliplatin (FOLFOX) and 5-fluorouracil/leucovorin/irinotecan (FOLFIRI), administered concurrently or sequentially, versus FOLFOX-BEV in first-line mCRC. Evaluation of biomarkers associated with treatment outcomes was an exploratory endpoint. Patients in the biomarker-evaluable population (BEP) had 1 tissue sample, 1 pre-induction plasma sample, and 1 post-induction plasma sample collected ≤60 days of induction from last drug date.Results:Among the 280 patients enrolled in STEAM, 183 had sequenced and evaluable tumor tissue, 118 had matched pre-induction plasma, and 54 (BEP) had ctDNA-evaluable sequencing data for pre- and post-induction plasma. The most common somatic variants in tumor tissue and pre-induction plasma were TP53, APC, and KRAS. Patients with lower-than-median versus higher-than-median post-induction mean allele fraction (mAF) levels had longer median PFS (17.7 vs. 7.5 months, HR, 0.33; 95% confidence interval, 0.17–0.63). Higher levels of post-induction mAF and post-induction mean mutant molecules per milliliter (mMMPM), and changes in ctDNA (stratified by a 10-fold or 100-fold reduction in mAF between pre- and post-induction plasma), were associated with shorter PFS. Post-induction mAF and mMMPM generally correlated with each other (ρ = 0.987, P < 0.0001).Conclusions:ctDNA quantification in post-induction plasma may serve as a prognostic biomarker for mCRC post-treatment outcomes.

Background SCLC is an aggressive disease with poor prognosis. Despite initial response to chemotherapy and radiotherapy, relapse occurs in most cases. To characterize genomic changes in SCLC over the course of therapy, we explored tracking tumor mutations in cell-free DNA (cfDNA) across post-treatment blood draws and comparing them to pre-treatment plasma and tissue profiles. Methods We retrospectively evaluated 235 samples collected from 24 subjects with late stage SCLC treated with first-line chemotherapy or chemoradiation in a prospective observational study. Tumor tissue samples were analyzed with the AVENIO Tumor Tissue Surveillance Kit (For Research Use Only, not for use in diagnostic procedures), a 198-kb next-generation sequencing panel covering 197 cancer genes. Matched peripheral blood mononuclear cells (PBMC), pre-treatment plasma, and multiple plasma from post-treatment timepoints were analyzed with the same panel using the AVENIO ctDNA Surveillance Kit (For Research Use Only, not for use in diagnostic procedures). A median input amount of 29 ng cfDNA, 129 ng tumor tissue DNA, and 50 ng PBMC DNA were sequenced to median deduplicated depths of 4491, 1315, and 6512, respectively. Somatic single nucleotide variants (SNVs) in tissue and plasma were identified by removing PBMC-matched germline or clonal hematopoietic mutations. Results We detected a median of 4 SNVs in tissue samples and a median of 100% (range 66 - 100%) of tissue SNVs in matched pre-treatment plasma. 96% (23/24) of subjects had at least one shared SNV between tissue and plasma, most commonly a TP53 mutation. A median of 7 SNVs were detected in pre-treatment plasma, whereas across all available post-treatment plasma (range 2 - 20 time points per subject), a median of 4 SNVs were detected. 53% of these mutations were not present in pre-treatment plasma or tissue. Conclusions Somatic mutations found in pre-treatment plasma were concordant with matched tissue, consistent with the highly metastatic nature of SCLC. ctDNA sequencing can provide additional molecular insights; in particular, detecting emergent mutations in ctDNA during treatment could advance our knowledge of SCLC. Legal entity responsible for the study Roche Sequencing Solutions, Inc. Funding Roche Sequencing Solutions, Inc. Disclosure S. Yaung: Full / Part-time employment: Roche. C. Woestmann: Full / Part-time employment: Roche. L. Xi: Full / Part-time employment: Roche. C. Ju: Full / Part-time employment: Roche. B. Hinzmann: Shareholder / Stockholder / Stock options, Full / Part-time employment: Roche. M. Thomas: Honoraria (institution), Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Roche. F. Lasitschka: Research grant / Funding (institution): Roche. M. Meister: Research grant / Funding (institution): Roche. M. Schneider: Research grant / Funding (institution): Roche. F.J.F. Herth: Honoraria (institution): Roche. T. Muley: Research grant / Funding (institution), Licensing / Royalties: Roche. B. Wehnl: Full / Part-time employment: Roche. J. Palma: Shareholder / Stockholder / Stock options, Full / Part-time employment: Roche. X.M. Ma: Shareholder / Stockholder / Stock options, Licensing / Royalties, Full / Part-time employment: Roche.

Background Microsatellite instability (MSI) is a hypermutable phenotype resulting from DNA mismatch repair deficiency and is observed in up to 10-15% of early-stage colorectal cancers (CRC). It manifests as abnormal lengthening or shortening of DNA repeats at specific genomic loci. MSI-High (MSI-H) CRC patients have been shown to respond favorably towards both chemotherapy and immunotherapy and have different prognosis than MSS patients and the FDA has approved Pembrolizumab as the first cancer therapy based on a class of biomarkers rather than a cancer type. With increasing options for targeted therapy in solid tumors, being able to combine MSI testing with other cancer biomarkers for approved therapies is beneficial. We show proof of concept of a pan-cancer gene panel using an NGS-based assay and bioinformatics workflow that enables classification of MSI status along with detection of SNVs, fusions, indels and CNVs from tumor tissue samples. Unlike the gold standard PCR-based test, our method does not require a matched normal sample, thus enabling MSI detection based on tumor tissue alone. Methods Our workflow combines whole genome library preparation, hybrid capture target enrichment, high-throughput sequencing and a proprietary analysis algorithm. We expanded the number of genomic loci to improve the sensitivity of MSI detection. The analysis algorithm was trained using DNA from pure and mixed cell lines, tumor tissue and normal samples with known MSI status to classify the molecular alterations between MSI-H and MSS genotypes from sequencing reads. The algorithm leverages repeat lengths in homopolymeric MSI loci in order to predict instability of individual loci followed by aggregation using a statistical framework to make the final call on MSI status. Results The above algorithm was evaluated on a cohort of 134 stage II and stage III CRC subjects who underwent curative intent surgery. MSI status for these samples was orthogonally tested using a PCR-based MSI Analysis System (31 positives, 103 negatives) and a dMMR system. Using a pre-determined threshold, the algorithm yielded 100% sensitivity and 100% specificity on the above cohort without using matched normal tissue. A second cohort evaluated includes 47 CRC patients that are enriched for MSI positive status by virtue of their selection criteria (BRAF positive). Very high concordance on MSI status with an orthogonal method was observed. Data demonstrating high concordance with a PCR_based MSI system will be available at the presentation. Conclusions Here we present an NGS-based assay and bioinformatics workflow with robust analytical performance for MSI detection in FFPE tissue samples without a paired normal. Citation Format: Amrita Pati, Hao Wang, Hamid Mirebrahim, Seng Saelee, Joshua Lefkowitz, Sean Chien, Ashla Singh, Fergal Casey, Vera Rapoport, Xiaoju Max Ma, John Lee, Alex Lovejoy, Daniel Klass, Hans-Peter Adams. Detecting microsatellite instability in ffpe tissue from crc subjects using next generation sequencing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4252.

e20701 Background: Quantifying circulating tumor DNA (ctDNA) is an emerging method to non-invasively assess treatment effect for solid tumors. Despite disease heterogeneity in NSCLC, we set out to identify a broadly applicable ctDNA-based method for disease monitoring. By employing plasma taken during early treatment cycles, we tested whether early response assessed by ctDNA level could predict treatment effect. Methods: Using a 197-gene NGS assay, the AVENIO ctDNA Surveillance Kit (For Research Use Only, not for use in diagnostic procedures), we measured ctDNA levels in post-treatment plasma samples based on variants identified at baseline. We used samples from an observational German Lung Cancer Multi-Marker Study. In a cohort of 83 stage IV lung adenocarcinoma treated with first-line chemo or chemoradiation therapies, we evaluated the association between survival and ctDNA levels in the first available post-treatment plasma sample (median number of days after start of treatment = 23). We used a ctDNA-based monitoring algorithm, and applied it to an independent set of 22 late stage lung squamous cell carcinoma (SCC) that also underwent chemo or chemoradiation therapies to further evaluate the algorithm in different histology subtypes. Results: We divided the 83 adenocarcinoma cohort into training (n = 53) and test (n = 30) sets. We found that subjects with longer progression free survival (PFS) had mean allele fraction (AF) < 1% in the training set. We applied the classifier to our validation set and found that subjects with mean AF < 1% had longer PFS (HR 0.35; 95% CI 0.12 - 0.93; log-rank P = 0.028) and overall survival (OS) (HR 0.29; 95% CI 0.09 - 0.89; log-rank P = 0.021). Using cutoffs identified in adenocarcinoma, we applied the same algorithms to the SCC cohort. Subjects with mean AF < 1% had longer PFS (HR 0.26; 95% CI 0.10 - 0.71; log-rank P = 0.005) and OS (HR 0.12; 95% CI 0.05 - 0.51; log-rank P = 0.001). Conclusions: Even in heterogeneous diseases such as NSCLC, changes in ctDNA levels in response to treatment may prove to be a valuable way of identifying subjects who may not benefit, which is earlier than current standard of care methods like computed tomography (CT) scan. Future prospective studies to confirm these results are warranted.

e18086 Background: The increasing adoption of Next Generation Sequencing (NGS) in molecular profiling of cancer presents a growing need for streamlined interpretation of NGS results in clinical labs. This can be achieved through bioinformatics tools equipped with a highly-curated database on clinically important variants. Methods: We performed an initial assessment of an NGS result interpretation tool called NAVIFY Mutation Profiler (NMP), which enabled us to process a Variant Call Format (VCF) file and generate a report with consensus recommendations of NCCN, ASCO, CAP and ACMG. This annotation tool identifies pathogenic variants and variants of unknown clinical significance (VUS), and groups variants by AMP Tiers. At the time of this assessment, NMP contained curation for ~4,000 variants. In this study, we used NGS results from 38 anonymized clinical cases with known treatment regimens to retrospectively assess NMP as the variant interpretation tool. Our cohort contained lung cancer subjects treated with EGFR tyrosine kinase inhibitor (TKI) (5 cases), as well as subjects relapsed against EGFR TKI (1 case) or ALK TKI crizotinib (22 cases). We also included 10 control cases where standard of care chemo was used because initial diagnostic methods did not reveal any actionable targets. Results: NMP annotated NGS VCF data and generated a report within 10 minutes per case although some cases contained > 100 variants. NMP correctly associated EGFR TKI therapies options with the corresponding 5 cases. As expected, NMP did not recommend targeted therapies for the 10 chemo-treated control cases. For the subject relapsed against EGFR TKI, NMP correctly interpreted the complex EGFR mutation profile containing both activating (L858R) and drug-resistance (T790M) variants. In addition, out of 22 cases relapsed against ALK TKI crizotinib, NMP correctly marked 14 with crizotinib resistance when a known ALK variant conferring crizotinib resistance was detected. There was limited or no published clinical evidence to interpret the remaining 8 cases of ALK TKI resistance. Conclusions: NMP correctly interpreted cases containing EGFR and ALK variants in this study. With a highly-curated knowledge base, this tool simplifies NGS clinical reporting by identifying clinically actionable mutations and associating treatment options qualified by supporting clinical evidence.

e14530 Background: Somatic variants found in plasma cell-free DNA (cfDNA) may derive from either solid tumors or clonal hematopoiesis (CH). Little is known about how this may impact plasma-based longitudinal disease monitoring using targeted sequencing of circulating tumor DNA (ctDNA). Methods: To assess the potential impact of CH in disease monitoring, we evaluated monitoring algorithms by targeted sequencing with and without matched peripheral blood mononuclear cells (PBMC). Samples were collected from a prospective observational study, where 62 late stage lung adenocarcinoma subjects were treated with first-line chemo or chemoradiation therapy. Pre-treatment plasma cfDNA and matched PBMC were analyzed with the AVENIO ctDNA Surveillance Kit (For Research Use Only, not for use in diagnostic procedures), a sequencing panel of 198 kilobases targeting cancer genes. Median input amounts of 25 ng cfDNA and 50 ng PBMC DNA were sequenced to median deduplicated depths of 4582 and 6134, respectively. Results: A median of 120 single nucleotide variants were detected per cfDNA sample, with 93.1% of these identified in matched PBMC. Most PBMC-matched cfDNA variants were germline SNPs, with allele frequency (AF) ~ 50% or 100%. A median of 1 (range 0-5) PBMC-matched cfDNA variants per sample were detected with an AF < 10%, consistent with CH. The number of these variants was positively associated with age (p-value = 0.0039) and the most frequently mutated gene was TP53. The remaining somatic variants (i.e., in cfDNA and not PBMC) had an AF range 0.03-40.9%. These PBMC-informed variants (median of 7 per sample) were used in longitudinal monitoring in the first post-treatment plasma sample to assess early response to therapy. Association between ctDNA level and progression-free survival using the same monitoring algorithm yielded nearly identical results on somatic variants derived from filtering approaches independent of matched PBMC (HR 0.32; 95% CI 0.16 - 0.65; log-rank P = 0.0009) and the PBMC-informed method (HR 0.31; 95% CI 0.14 - 0.66; log-rank P = 0.0013). Conclusions: A targeted panel focused on solid tumors by design has limited impact from CH. For disease monitoring applications in a non-MRD setting, measuring multiple variants instead of a single variant further enables robust classifiers that can moderate the impact of variants, if any, from CH.

The evolutionarily conserved serine-threonine kinase mammalian target of rapamycin (mTOR) plays a critical role in regulating many pathophysiological processes. Functional characterization of the mTOR signaling pathways, however, has been hampered by the paucity of known substrates. We used large-scale quantitative phosphoproteomics experiments to define the signaling networks downstream of mTORC1 and mTORC2. Characterization of one mTORC1 substrate, the growth factor receptor-bound protein 10 (Grb10), showed that mTORC1-mediated phosphorylation stabilized Grb10, leading to feedback inhibition of the phosphatidylinositol 3-kinase (PI3K) and extracellular signal-regulated, mitogen-activated protein kinase (ERK-MAPK) pathways. Grb10 expression is frequently down-regulated in various cancers, and loss of Grb10 and loss of the well-established tumor suppressor phosphatase PTEN appear to be mutually exclusive events, suggesting that Grb10 might be a tumor suppressor regulated by mTORC1.

12045Background: Studies show that mutation count can be used as a biomarker to predict whether or not a patient may respond to immunotherapy or chemoradiation therapy. However, mutation count is u...

12077Background: Longitudinal ctDNA monitoring using variants identified in tissue biopsies is an emerging method for disease management. However, tissue biopsy is often inaccessible for many late ...

12088Background: Despite routine use of chemotherapy in advanced non-small-cell lung cancer (NSCLC) patients, the knowledge of optimal prognostic methods is still limited to imaging-based methods. ...

SummaryDifferent protein complexes form on newly spliced mRNA to ensure the accuracy and efficiency of eukaryotic gene expression. For example, the exon junction complex (EJC) plays an important role in mRNA surveillance. The EJC also influences the first, or pioneer round of protein synthesis through a mechanism that is poorly understood. We show that the nutrient-, stress-, and energy-sensing checkpoint kinase, mTOR, contributes to the observed enhanced translation efficiency of spliced over nonspliced mRNAs. We demonstrate that, when activated, S6K1 is recruited to the newly synthesized mRNA by SKAR, which is deposited at the EJC during splicing, and that SKAR and S6K1 increase the translation efficiency of spliced mRNA. Thus, SKAR-mediated recruitment of activated S6K1 to newly processed mRNPs serves as a conduit between mTOR checkpoint signaling and the pioneer round of translation when cells exist in conditions supportive of protein synthesis.

The BCL-2/BCL-XL/BCL-W inhibitor ABT-263 (navitoclax) has shown promising clinical activity in lymphoid malignancies such as chronic lymphocytic leukemia. However, its efficacy in these settings is limited by thrombocytopenia caused by BCL-XL inhibition. This prompted the generation of the BCL-2-selective inhibitor venetoclax (ABT-199/GDC-0199), which demonstrates robust activity in these cancers but spares platelets. Navitoclax has also been shown to enhance the efficacy of docetaxel in preclinical models of solid tumors, but clinical use of this combination has been limited by neutropenia. We used venetoclax and the BCL-XL-selective inhibitors A-1155463 and A-1331852 to assess the relative contributions of inhibiting BCL-2 or BCL-XL to the efficacy and toxicity of the navitoclax-docetaxel combination. Selective BCL-2 inhibition suppressed granulopoiesis in vitro and in vivo, potentially accounting for the exacerbated neutropenia observed when navitoclax was combined with docetaxel clinically. By contrast, selectively inhibiting BCL-XL did not suppress granulopoiesis but was highly efficacious in combination with docetaxel when tested against a range of solid tumors. Therefore, BCL-XL-selective inhibitors have the potential to enhance the efficacy of docetaxel in solid tumors and avoid the exacerbation of neutropenia observed with navitoclax. These studies demonstrate the translational utility of this toolkit of selective BCL-2 family inhibitors and highlight their potential as improved cancer therapeutics.

The process of translation requires substantial cellular resources. Cells have therefore evolved complex mechanisms to control overall protein synthesis as well as the translation of specific mRNAs that are crucial for cell growth and proliferation. At the heart of this process is the mammalian target of rapamycin (mTOR) signalling pathway, which senses and responds to nutrient availability, energy sufficiency, stress, hormones and mitogens to modulate protein synthesis. Here, we highlight recent findings on the regulators and effectors of mTOR and discuss specific cases that serve as paradigms for the different modes of mTOR regulation and its control of translation.

Abstract 1057 Poster Board I-79 The PI3K-Akt signal transduction pathway plays a key role in the pathogenesis of many human cancers. In AML malignancy, deregulation of upstream receptor tyrosine kinases such as FLT3, c-Kit, and c-FMS or mutations in K-Ras, N-Ras, B-Raf and CEBPA genes lead to activation of PI3K-Akt signaling to promote cell survival and cell growth. A highly selective Class I PI3K inhibitor, GDC-0941, provides exciting therapeutic opportunities for targeting this pathway in AML. Here we show that GDC-0941 significantly inhibits the viability of the majority of a large panel of AML cell lines tested in vitro (80% or 19/24) at a concentration of < 1 uM. Because not all AML cell lines responded to GDC-0941, we show that PI3K-Akt pathway activation, evidenced by basal pAkt level, can serve as a potential predictive biomarker for GDC-0941 in AML in that sensitive cell lines displayed higher level of pAkt relative to resistant cell lines. Consistently, GDC-0941 treatment leads to decreased pAkt, and therefore the down-regulation of this important pro-survival signaling. Our further analysis shows that GDC-0941 treatment can induce apoptosis and/or cell cycle arrest. We also obtained fresh AML tumor samples to test whether GDC-0941 can similarly induces apoptosis in blast cells and showed that GDC-0941 treatment results in a down-regulation of pAkt level and increased apoptosis. Other PD biomarkers such as phospho-BAD level and Bim expression are both consistent with the observed apoptotic responses. Furthermore, the mammalian target of rapamycin complex 1 (mTORC1) inhibitor, rapamycin, synergizes with GDC-0941 to produce an increased amount of apoptosis in several AML cell lines tested. This is likely due to the fact that long-term treatment with rapamycin induces the sensitivity of the PI3K –Akt signaling pathway by releasing the negative feedback loop of mTORC1-S6K-IRS1/2 module. Importantly, in some AML cell lines we observe synergies between GDC-0941 and AraC. Interestingly, while AraC alone does not induce apoptosis in AML cell lines with PTEN loss or mutation, the synergy between AraC and GDC-0941 comes from increased apoptotic response, suggesting that GDC-0941 can synergize with chemo agents that induces S/G2 cell cycle arrest. Together, our preclinical data suggest that GDC-0941 may be used as a targeted therapy in AML patients as a single agent or in combination with other chemotherapies in clinic. Disclosures: Ma: Genentech Inc.: Employment. Du:Genentech, Inc.: Employment, Equity Ownership. Sun:Genentech Inc.: Employment. Shi:Genentech, Inc.: Employment, Equity Ownership. Friedman:Genentech Inc.: Employment. Dornan:Genentech, Inc.: Employment, Equity Ownership. Ebens:Genentech, Inc.: Employment, Equity Ownership, Patents & Royalties.

Abstract 3787 Poster Board III-723 Acute myeloid leukemia (AML) is a biologically and molecularly heterogeneous malignancy characterized by an accumulation of myeloid-lineage cells in the blood and bone marrow. Phosphatidylinositol 3' kinase (PI3K) -mediated signaling is frequently dysregulated in cancer and controls fundamental cellular functions such as cell migration, growth, survival and development of drug resistance in many cancers, including AML, and therefore represents an attractive therapeutic target, even against the backdrop of AML disease heterogeneity. In AML, for example, activating mutations in Ras and Flt3 are common and a number of autocrine and paracrine signaling mechanisms have been proposed as important disease mediators; all converge on PI3K as an important signal transduction node to provide growth- and survival-promoting effects. Here, we demonstrate that PI3K p110-a,b,d catalytic subunits are all prevalent across a panel of ∼30 cell lines and that the majority of cell lines as well as primary patient samples show evidence of PI3K pathway activation. We demonstrate in vitro with both cell lines and patient cell isolates, that a potent and selective pan-isoform PI3K inhibitor, GDC-0941, modulates pharmacodynamic markers such as p-Akt, p-4E-BP1, and p-FOXO-3a, and that treated cells show a G0/G1 cell-cycle arrest. A strong induction of apoptosis is observed by annexin/PI staining with upregulation of cleaved caspases and PARP. Preliminary observations suggest significant induction of p27 and Bim as direct transcriptional targets of FOXO-3a, as well as downregulation of c-Myc levels; these targets may represent key mediators of observed cellular effects and are the subject of ongoing work. Additional studies are currently underway to identify clinical standard-of-care agents and new molecular entities (pipeline NMEs) that combine favorably with PI3k-inhibition in vitro, and the results of several in-vivo xenograft studies will also be presented. Disclosures: Sun: Genentech Inc.: Employment. Berry:Genentech: Employment, Patents & Royalties. Du:Genentech, Inc.: Employment, Equity Ownership. Ma:Genentech: Employment, Patents & Royalties. Shi:Genentech: Employment, Patents & Royalties. Medeiros:Genentech: Research Funding. Ebens:Genentech, Inc.: Employment, Equity Ownership, Patents & Royalties.