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68 Background: HER2 amplification is an emerging biomarker in colorectal cancer (CRC) with increased copy number associated with improved clinical outcomes to HER2 targeting. RAS/RAF wildtype CRC also benefit from use of epidermal growth factor receptor inhibition (EGFRi). The sequencing of EGFRi versus HER2 inhibition in low copy number HER2 amplified CRC remains uncertain. Patient-derived cancer organoids (PDCOs) allow an ex vivo method to assess treatment sensitivity. We examined treatment sensitivity of a HER2 amplified PDCO at baseline and following resistance to panitumumab and trastuzumab. Methods: Following IRB-approval, fresh CRC tissue was cultured to maturation. After expansion, subcultures were treated with stepwise (20%) increase to physiologic Cmax of panitumumab (230ug/mL) and trastuzumab (180ug/mL). Threshold for escalation was median relative growth of +20% at 96h. Sensitivity was assessed on primary culture (RC1), panitumumab resistance (RC1-P) and trastuzumab resistance (RC1-T) using 96h of physiologic Cmax panitumumab, trastuzumab, and combination trastuzumab/pertuzumab. Individual sphere response was assessed for change in mean NADH autofluorescence intensity and ratio of NADH/FAD signal. Response was assessed at 96h in comparison to control using effect size of Glass’s Delta (GΔ). Results: Molecular profiling revealed HER2 copy number of 14 with no concurrent alterations in RAS, RAF, or PIK3CA. Time to resistance was similar between panitumumab (55 days) and trastuzumab (51 days). RC1 had baseline growth (+116%) which was reduced with single agent panitumumab (+17%, GΔ=1.40) with intermediate sensitivity to trastuzumab (+48%, GΔ=0.95) and trastuzumab/pertuzumab (46%, GΔ=0.99). Normalized NADH/FAD ratio revealed significant metabolic response to panitumumab (-20%, GΔ=0.66) and trastuzumab/pertuzumab (-35%, GΔ=1.16) with insignificant effect of single agent trastuzumab (-14%, GΔ=0.46). Following resistance to panitumumab, RC1-P had persistent growth with trastuzumab (+68%) which improved in combination trastuzumab/pertuzumab (+34%, GΔ=1.16). Following resistance to trastuzumab, RC1-T was insensitive to EGFRi with panitumumab including persistent growth (+58%, GΔ=0.70) and unchanged metabolism (+2%, GΔ=-0.10). Conclusions: Therapeutic dose escalation in a single PDCO of HER2 amplified CRC suggests improved sensitivity to EGFRi and dual HER2 targeting with trastuzumab/pertuzumab. Resistance to EGFRi resulted in persistent sensitivity to dual HER2 inhibition using trastuzumab/pertuzumab, however resistance to single agent trastuzumab. Resistance to trastuzumab resulted in future insensitivity to EGFRi. Molecular profiling at resistance revealed no pathologic alterations in EGFR or ERBB2 signaling, with ongoing analysis of transcriptional changes by RNAseq.

177 Background: No current clinical tool can predict the efficacy of cancer therapeutics for patients with colorectal cancer (CRC). We recently demonstrated the feasibility of using patient-derived cancer organoids (PDCOs) to examine therapeutic response and tumor heterogeneity for individual patients with CRC via optical metabolic imaging (OMI). Here we expand these analyses in a cohort of patients with clinical outcomes. Methods: CRC tissue was collected from patients on IRB-approved protocols. PDCOs were matured and treated with chemotherapy regimens concurrent with patient treatment. Previously established effect size response thresholds were used for diameter ( > 1.5) and OMI ( > 0.5) following 48 hours of treatment. OMI measures the intrinsic autofluorescence of NAD(P)H and FAD using 2-photon microscopy without specific reagents or dyes. Clinical outcomes were prospectively collected by manual chart review. Results: 12 CRC PDCOs were established from patients with CRC. PDCOs were collected from initial diagnosis and advanced setting of both primary and metastatic sites by core needle biopsy and surgical resection. Differential growth rates were observed across lines. PDCOs with RAS/RAF alterations had more uniform growth, while PDCOs without these alterations demonstrated more heterogeneous growth and metabolism. Clinical correlation of PDCOs response with recurrence of disease in the adjuvant setting will be presented. Cases with prior 5-FU-based chemotherapy at the time of PDCO collection had intermediate sensitivity. For PDCOs collected pre-treatment, PDCO response predicted clinical response for 5 of 6 cases using predefined sensitivity thresholds. In the case that overall PDCO response did not predict clinical response, a heterogenous response was observed with distinct sensitive and resistant populations. Across PDCOs, greater post-treatment heterogeneity was observed in resistant lines compared to those with treatment sensitivity. Conclusions: Tumor heterogeneity in treatment response can be assessed using PDCOs growth and metabolism. The utility of PDCOs to predict clinical outcomes for patients with CRC deserves further prospective validation.

OBJECTIVE: Cancer treatment is limited by inaccurate predictors of patient-specific therapeutic response. Therefore, some patients are exposed to unnecessary side effects and delays in starting effective therapy. A clinical tool that predicts treatment sensitivity for individual patients is needed. DESIGN: Patient-derived cancer organoids were derived across multiple histologies. The histological characteristics, mutation profile, clonal structure, and response to chemotherapy and radiation were assessed using bright-field and optical metabolic imaging on spheroid and single cell-levels, respectively. RESULTS: We demonstrate that patient-derived cancer organoids represent the cancers from which they were derived, including key histologic and molecular features. These cultures were generated from numerous cancers, various biopsy sample types, and in different clinical settings. Next-generation sequencing reveals the presence of subclonal populations within the organoid cultures. These cultures allow for the detection of clonal heterogeneity with a greater sensitivity than bulk tumor sequencing. Optical metabolic imaging of these organoids provides cell-level quantification of treatment response and tumor heterogeneity allowing for resolution of therapeutic differences between patient samples. Using this technology, we prospectively predict treatment response for a patient with metastatic colorectal cancer. CONCLUSION: These studies add to the literature demonstrating feasibility to grow clinical patient-derived organotypic cultures for treatment effectiveness testing. Together, these culture methods and response assessment techniques hold great promise to predict treatment sensitivity for patients with cancer undergoing chemotherapy and/or radiation. STATEMENT OF TRANSLATIONAL RELEVANCE: The lack of predictive biomarkers is a major limitation in clinical oncology. Patient-derived cancer organoids are a major advance as they are readily generated and represent the tumors from which they are derived. This study further demonstrates the ability of these cultures to represent the phenotypic and molecular heterogeneity within cancers. In addition, this study establishes therapeutic thresholds for further validation using changes in organoid growth rate and optical metabolic imaging. These techniques measure organoid-level and single cell-level therapeutic heterogeneity, respectively. Here these techniques are applied for determining differential response of colorectal cancers to chemotherapy and radiation. In addition, this is one of the first studies to prospectively examine the use these cultures to predict response for an individual patient with cancer.

Background: Colorectal cancer (CRC) remains the second leading cause of cancer-related mortality with limited precision strategies. The human epidermal growth factor receptor (HER2) is amplified in 5% of patients with metastatic CRC. Therapeutic studies have demonstrated activity of HER2 targeting regimens in the late-line treatment setting though little characterization has been done in the setting of not having prior anti-epidermal growth factor receptor antibody therapy or in the first-line treatment setting. Methods: Patient with metastatic colorectal cancer underwent next-generation sequencing (NGS) panel testing by Strata Oncology through the University of Wisconsin Precision Medicine Molecular Tumor Board. Patients were treated per multi-disciplinary recommendation across multiple lines of therapy and tracked by prospective registry (IRB#UW15068). HER2 copy numbers >/= 10 were used to determine amplification. A subset of patients with HER2-amplified CRC were treated with single agent trastuzumab. Results: HER2 amplifications were identified in 4 of 78 cases of metastatic CRC (5.1%). All biopsies were performed prior to exposure to anti-epidermal growth factor receptor inhibitors. Median estimated copy number (CN) was 55.5 [range 13-178]. There was no concurrent alterations in extended RAS, BRAF, PIK3CA, AKT or MTOR. All cases included concurrent mutations in TP53 at R175H (2), C135W, or C135F. Single agent trastuzumab was administered to two patients at standard dosing (trastuzumab 8mg/kg intravenous day 1 cycle 1 followed by 6 mg/kg intravenous day 1 cycle 2+ on a 21 day cycle). One patient was treated in the treatment refractory setting. They had resolution of bowel obstructive symptoms and a minor response on imaging. Additionally, a patient with a HER2 amplification (CN 178) was treated in the first-line setting with single agent trastuzumab. The patient had grade 1 fever with the first cycle and no other treatment related adverse events thereafter. The patient’s CEA decreased from 7,506 to 2,525 ng/mL with the first cycle of therapy and overall reduced to 6.5 ng/mL after 12 cycles of therapy. The patient has had a partial response per RECIST v1.1 response criteria with a reduction of cross-sectional diameter of their disease by 60%. The patient currently continues on this therapy without evidence of disease progression. Conclusions: HER2 amplified colorectal cancers are an important subtype of colorectal cancer. Here we describe the potential benefit of HER2 targeting with single agent trastuzumab and even demonstrate single agent activity in the first-line setting. Further studies should be done to further characterize the benefit of this low toxicity treatment option for patients with metastatic HER2 amplified colorectal cancer. Citation Format: Jeremy Kratz, Nataliya Uboha, Kayla Lemmon, Hannah Houtler, Mark Burkard, Dustin Deming. Durable response to first-line Trastuzumab in HER2 amplified colorectal cancer [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 1414.