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e20516 Background: GGO-associated pulmonary nodule has been known as radiological appearances of early stage and exhibit more indolent biological behavior. The correlation of different driver gene and radiological features remain poorly understood. Methods: We performed high-depth sequencing of 334 resected pulmonary nodules presenting as GGO from 262 Chinese patients with a custom 1021-gene panel. 130 were multiple pulmonary nodules from 58 patients (2-4 samples per patient). Clinical-pathologic and radiologic parameters of these pulmonary nodules were collected. Immunohistochemistry and multiplex immunofluorescent staining were applied to analyze proliferation and immune cell markers of GGO-associated pulmonary nodules. Results: Mixed GGO enriched in the pathology of invasive LUAD comparing to pure GGO (182/216 vs 73/118, p < 0.001). 88.0% (294/334) of GGO-associated nodules carried at least one gene mutation in EGFR/ERBB2/BRAF/KRAS/MAP2K1 of the RTK/RAS signaling pathway and these driver genes were mutual exclusive to each other. T790M mutation was detected in one patient who had a nodule with CTR > 0.5 and was pathologically defined as MIA. 96.4% (54/56) multiple pulmonary nodules from the same patients showed distinct oncogenic alterations, but 72.4% (42/58) patients carried at least one mutant gene in RTK/RAS pathway across each pulmonary nodule. Nodules with ERBB2/ BRAF/ MAP2K1 mutations tended to be more indolent than those with EGFR and KRAS mutations, showing fewer mutations in radiology status of mGGO or pathology of invasive LUAD. KRAS-mutant subgroup possessed the highest expression of Ki-67 and PD-L1, more infiltration of CD4+ T cell and CD8+T cell. The second highest Ki67-expression was in EGFR-mutant subgroup, together with more CD8+T cell. For EGFR-mutant nodules, co-mutations with TP53 or RBM10 enriched in nodules with CTR > 0.5 and showing higher values of mean CT attenuation and TMB, which may relate to GGO evolution or invasiveness progression. Conclusions: This study elucidated a comprehensive genomic landscape of Chinese radiologically detected GGO-associated pulmonary nodules and highlighted different driver patterns of RTK/RAS pathway corresponding to radiologic features. Our findings provided valuable insight for further research on driver event of RTK/RAS pathway and cancer interception of GGO-associated pulmonary nodules.

3612 Background: NF1-related PN are locally invasive tumors characterized by increased activation of the RAS pathway causing significant morbidity including disfigurement, pain and functional limitations. Selumetinib has received breakthrough designation for NF1 PN based on phase I / II trials in children. We present results for the ongoing phase II study of selumetinib in adults with NF1 PN, which includes pharmacodynamic (PD) evaluation of serial tumor biopsies as well as functional/patient-reported outcomes (PROs). Methods: Open-label Simon 2-stage design. Eligibility: NF1 patients (pts) ≥18 years old with inoperable/symptomatic/progressive PN. First 2 pts received selumetinib 75 mg BID; subsequent pts received selumetinib 50 mg BID. Primary objective: response rate by volumetric MRI analysis (partial response [PR]; ≥20% volume decrease). Secondary objectives: PD studies on pre/on-treatment biopsies of PN and cutaneous neurofibromas, assessment of clinical benefit using PROs (Numeric Rating Scale-11, Pain Interference Index), and PN-specific functional assessments. Validated, fit-for-purpose, isozyme-specific measurements of pERK/ERK/pMEK/MEK performed using SOPs designed for labile phosphoproteins (PMID 27001313). Results: As of February 2020, 27 pts have enrolled. Outcomes are reported for 23 pts (74% male; median age 33 years, range 18-60). Most common PN-related morbidity: pain (19 pts). Sixteen pts achieved PR (69%), with 13/16 confirmed; no disease progression. Time to response: 11 months (range 5-25); median change in PN volume at best response: -22% (range -41% to +5.5%); median duration of treatment: 28 months (range 2-50). Selumetinib suppressed tumor pERK1,2/ERK1,2 but not pMEK1,2/MEK1,2 ratios from 1-10 hours following oral dosing (one t½). Pt-reported target tumor pain intensity and pain interference scores significantly improved (both p < 0.03). Pts 1 and 2 were dose-reduced due to grade 3 intolerable rash (n = 2) and pain (n = 1). Grade ≥3 drug-related toxicities on 50 mg (21 pts) include transaminitis (5 pts), rash (1 pt) and pancreatic enzyme elevation (1 pt). Two pts were dose reduced (rash = 1 pt, transaminitis = 1 pt). Two pts discontinued by choice, 2 pts withdrawn by PI (best interest of patient), and 1 pt each removed for transaminitis, surgical resection, serious concurrent medical illness, and non-compliance. Conclusions: Selumetinib shrinks the majority of adult PN and results in molecular target suppression and clinical benefit. Clinical trial information: NCT02407405 .

e13562 Background: Neurofibromatosis type 1 (NF1) is caused by mutations of the tumor suppressor gene NF1 resulting in decreased levels of neurofibromin and dysregulation of the RAS pathway, including MEK/ERK upregulation. NF1 is characterized by multiple benign and malignant tumors. Central nervous system tumors have an overall standardized incidence ratio of 37.5 in population studies with high rates of aggressive gliomas in adults with NF1. The response to standard glioma therapies is mixed. MEK1/2 inhibitors have shown activity in NF1 driven plexiform neurofibromas and low grade gliomas, however, data is lacking about the optimal dose or sequencing of MEK1/2 inhibitors for adults with NF1 associated aggressive gliomas. We present recent experiences with the MEK1/2 inhibitor trametinib in adults with NF1 and aggressive gliomas. Methods: A retrospective chart review was conducted on all adult patients with NF1 and astrocytoma treated with trametinib at the Johns Hopkins Brain Cancer Program between 2016-2018. Results: Three patients met selection criteria. Two received trametinib as initial therapy (2 mg daily). All developed an acneiform rash; one had transient transaminitis requiring temporary discontinuation and subsequent dose reductions. Clinical benefit was achieved associated with two partial radiographic responses. Conclusions: Astrocytomas in adults with NF1 often have a more aggressive course than suggested by histology. The cases presented here demonstrate clinical benefit from single agent MEK inhibition as well as possible synergistic effects with conventional therapies for gliomas in this patient population. These observations highlight the need for further research in this area. [Table: see text]

e14638 Background: Breast cancer is the highest incidence malignancies in women worldwide. Luminal breast cancers are typically estrogen receptor–positive with better prognosis. However, the rapid disease progression and the high relapse rate of this subtype of breast cancer have become a puzzle in breast cancer treatment. It gave us the motivation to figure out the anomalous molecular mechanism which devoted in. It has been well-documented that the RAS pathway is overloadly activated in more than half of human breast tumors. RAS genes encode a superfamily of small GTPases that contribute to cell growth signals. Methods: Gene expression level were measured by qPCR and Western Blot.Biological effects of each condition were evaluated in cell viability and migration. Results: In this study, we investigated one member of the RAS family, RERG, which was related to the ER pathway and contributed to inhibit Ras activated pathway. Our results showed that knockdown of RERG concomitantly promoted two major oncogenic pathways, Ras and Stat3 signaling pathways, in luminal type breast cancer cell lines. Moreover, ectopic RERG expression significantly inhibited Ras expression. It implicated that RERG mediated in RAS-driven biological effects. Our findings indicated that knockdown of RERG enhanced mobility of the breast cancer cells and made cells more intractable under SERM treatment. Conclusions: We elucidated the tumor-suppressor role of RERG in breast cancer cells though inhibition of the Ras and Stat3 signaling pathways. Therefore, this study might shed light on the important mechanistic insight into the tumorigenesis of ER-positive luminal type cancer and provided the prognostic and therapeutic improved roles of RERG.

679 Background: Mutational activation of the RAS pathway occurs in >50% of human CRC tumors, and to date has been difficult to overcome. We recently identified receptor tyrosine phosphatase-S (PTPRS) as an important regulator of the RAS pathway, which is mutated in ~11% of CRC. Methods: Global gene expression and DNA sequencing data (1321 cancer genes) were integrated across 468 CRC tumors to identify PTPRS as one of the most commonly mutated genes with a high correlation to a RAS activation score. Apoptotic responses to inhibitors of ERK, EGFR and their combination were tested in isogenic wild-type and mutant RAS cell lines where PTPRS had been knocked out by CRISPR. Results: PTPRS was in the top 15 genes correlating with RAS pathway activation scores; as expected, KRAS, BRAF were the most correlated genes. In order to determine the effect of the loss of PTPRS on RAS/ERK signaling, we used CRISPR to knockout PTPRS in an isogenic pair of CRC cell lines (HCT116) with mutant or wild type KRAS. Cell lines lacking PTPRS expression had elevated phospho-ERK activity. Interestingly, cell lines with PTPRS knockout and elevated ERK phosphorylation had an increased sensitivity to ERK inhibitors. Moreover, the loss of PTPRS allowed ERK to localize to the nucleus. Apoptosis increased dramatically from 13.1% in control cells to 53.8% in PTPRS KO cells treated with both ERK and EGFR inhibitors (Table), a synergistic effect not seen in wild type KRAS cells, where only ERK inhibitors were active. Conclusions: The loss of PTPRS allows increased activation of ERK (and the RAS pathway) which is associated with ERK addiction and increased sensitivity to ERK inhibitors. Surprisingly, ERK inhibitors synergize with EGFRi in wild type KRAS cell lines absent PTPRS. These data suggest the potential for mutant PTPRS to serve as a biomarker for ERK/EGFR inhibition. [Table: see text]

e17073 Background: Locally advanced HPV+ oropharynx cancer (OPC) patients have a remarkable good outcome. However, the frequency of distant metastases (DM) is similar to HPV – cases. Some clinical ...

3544 Background: Cetuximab was approved for treating EGFR-expressing metastatic colorectal carcinoma (mCRC) without patient stratification. Subsequent retrospective clinical studies resulted in an exclusion criterion for patients with KRAS mutations at codons 12 and 13. However, only a fraction of patients with wtKRAS benefit from the treatment. Recent analyses indicated that patients with KRAS mutation at codon 13 can also benefit. We set out to investigate whether KRAS mutations, or any other factors, are good biomarkers for CRC-cetuximab therapy patient stratification. Methods: We have established patient derived xenografts (PDX) from treatment-naive Asian CRC patients to discover biomarker predictive of cetuximab response. We conducted a clinical trial style study (“patient avatar trial”) of cetuximab using a randomly selected cohort of 26 EGFR+ PDXs. The antitumor activities were analyzed against KRAS mutation status and a published expression-signature. Results: We identified 12/26 (~46%) as cetuximab responders and 14/26 non-responders (defined by 50% tumor growth inhibition threshold). All 14 non-responders are mutated for one or more of KRAS, BRAF (V600E), EGFR, AKT and PIK3CA oncogenes. In contrast, 5/11 responders analyzed are wild-type for all these genes. Importantly, 5/11 responders have activating KRAS mutations at codons 12/13, contradictory to the currently practiced clinical exclusion criteria, but consistent with more recent clinical findings. Most interestingly, the observed cetuximab activity in this cohort of 26 PDXs has a surprisingly strong correlation to a published RAS pathway score. Conclusions: Our results indicated strong predictive power of cetuximab-CRC-PDX trial and RAS signature, and warrant prospective clinical studies for further confirmation.

3573 Background: JX-594 is a first-in-class targeted oncolytic poxvirus designed to selectively replicate in and destroy cancer cells with cell cycle abnormalities and EGFR/ ras pathway activation....

14128 Background: ECO-4601 is a structurally novel farnesylated dibenzodiazepinone with broad μM in vitro cytotoxic activity, and in vivo antitumor efficacy in rat glioma, hormone-independent human prostate, breast tumor xenograft tumor models. Preclinical data suggest ECO-4601 is a targeted anticancer drug with dual activity: selective binding to the peripheral benzodiazepine receptor (PBR), resulting in apoptosis, and inhibition of the Ras-MAPK pathway. Greatest efficacy was observed with continuous exposure, and a target plasma ECO-4601 efficacy concentration was determined. Preclinical toxicity studies did not demonstrate significant or dangerous side-effects. ECO-4601 is currently in phase I clinical trial testing to determine toxicity, pharmacologic profile and antitumor efficacy. Methods: ECO-4601 is administered as a 2-week continuous i.v. infusion (CIV), followed by 1 week off in repeated 21 day cycles. The trial includes dose- escalation and dose-extension portions, with comprehensive pharmacokinetics (PK) during the first cycle. Dose-escalation consists of increased doses in single pts until grade 3 toxicity is observed during cycle 1 of treatment, with up to five additional pts dosed to confirm dose-limiting toxicity (2/6 pts with grade 3 toxicities). The extension portion includes up to 15 pts at the dose determined in the first portion. Patients with a variety of cancers have been treated, including colorectal (10), ovarian (2), duodenal (1), and glioma (1). Results: ECO-4601 doses of 30, 60, 120, 180, 270, 360, and 480 mg/m2/day were evaluated in 14 patients. The number of cycles ranged from 1 to 8 with 7 pts completing at least 3 cycles of treatment. ECO-4601 is well tolerated and a maximum tolerated dose (MTD) has not been reached. Stable disease was observed in 6 of 7 evaluable pts; 4 colorectal, 1 ovarian, 1 duodenal. Preliminary PK shows steady state concentrations following 24 h CIV, dose proportionality, plasma concentrations above the preclinical efficacy threshold, rapid elimination post-infusion. Conclusions: ECO-4601 is a bifunctional targeting agent, against a novel combination of targets, that is well tolerated and demonstrates evidence of biological activity in an early phase clinical trial. The extension portion is currently ongoing. [Table: see text]