bTMB-High Basket trial: A multicenter phase II trial of nivolumab monotherapy in patients with advanced gastrointestinal cancers with high blood tumor mutational burden (bTMB)

TPS179

Background: Tumor mutational burden (TMB) is an emerging biomarker for immune checkpoint inhibitors (ICIs) in non-small cell lung cancer (NSCLC). Analysis of circulating tumor DNA (ctDNA) has been reported to effectively identify patients likely to respond to ICIs by effectively and non-invasively evaluating the TMB in the tumor in NSCLC and gastric cancer. Methods: We are conducting an investigator-initiated multicenter phase II basket trial to investigate efficacy and safety of nivolumab monotherapy in patients with advanced gastrointestinal (GI) cancers with high bTMB identified by ctDNA analysis as part of the Nationwide Cancer Genome Screening Project (SCRUM-Japan GI-SCREEN). Eligibility criteria include histologically confirmed unresectable or recurrent GI malignancies; ECOG PS of 0 or 1; refractory or intolerant to the standard therapies; and high bTMB identified by a 73-gene sequencing ctDNA panel (Guardant360) regardless of microsatellite instability status. Patients will be enrolled into one of four disease-specific cohorts (colorectal, gastric, esophageal, and other GI cancer cohort), and receive intravenous nivolumab monotherapy of 360 mg every 3 weeks. The bTMB score is calculated by adjustment of mutation count by tumor fraction, and tentative bTMB level cut-offs were determined according to objective response rate (ORR) reported for ICI treatment for each tumor subtype in previous trials. The trial will utilize a two-stage design with a Bayesian hierarchical model, and tentative bTMB level cut-off will be re-assessed in the first stage. Primary endpoint in each stage is the disease control rate at 6 week and the ORR assessed by investigators per RECIST v1.1, respectively. Target sample size is determined as 70 in total so that the statistical power in each disease-specific cohort calculated based on a Bayesian posterior distribution attains 70 to 80% with one-sided alpha level in each cohort of approximately 10%. For biomarker analysis, tumor tissue and ctDNA will be serially collected and analyzed by whole-exome, transcriptome, and T cell receptor sequencing. This trial was initiated since September 2018. Clinical trial information: UMIN000033182.

Leukocytoclastic vasculitis with purpura and renal failure induced by the anti-epidermal growth factor receptor antibody panitumumab: a case report

Background

Panitumumab is the first human combinatorial antibody for the treatment of metastatic colorectal carcinoma. Dermatologic toxicity of all grades occurs in more than 90% of patients. However, there are few reports of purpura induced by anti-epidermal growth factor receptor antibody. Renal failure is also uncommon as an adverse event of anti-epidermal growth factor receptor antibody.

Case presentation

A 67-year-old Japanese man with advanced colon cancer received monotherapy with panitumumab. General malaise, bilateral edema of his legs, and bilateral purpura of his forearms developed 2 days after the second cycle of panitumumab. A skin biopsy was performed to evaluate the purpuric lesions on his left leg and leukocytoclastic vasculitis was diagnosed. Blood tests showed grade III acute renal failure with a blood urea nitrogen level of 33.8 mg/dL and a creatinine level of 3.10 mg/dL.

Conclusions

This is the first reported case of leukocytoclastic vasculitis followed by purpura and acute renal failure associated with panitumumab.

Clinical significance of intratumoral HER2 heterogeneity on trastuzumab efficacy using endoscopic biopsy specimens in patients with advanced HER2 positive gastric cancer

BACKGROUND

We recently reported the clinical significance of intratumoral HER2 heterogeneity on trastuzumab efficacy using surgical specimens; patients with homogeneously HER2 positive gastric cancer benefitted more from trastuzumab. However, the majority of patients are diagnosed by endoscopic biopsy, and surgical specimens are not available in these patients. The aim of this study is to verify clinical significance of HER2 heterogeneity on trastuzumab efficacy using biopsy specimens.

METHODS

Eighty-seven patients, who received trastuzumab-based chemotherapy and whose endoscopic biopsy specimens were available for HER2 assessment, were consecutively enrolled. When all tumor cells in all biopsy specimens overexpressed HER2 protein, it was defined as homogeneously HER2 (homo-HER2) positive group, and the others were defined as heterogeneously HER2 (hetero-HER2) positive group. Progression-free survival (PFS), overall survival (OS) and objective response rate (ORR) were evaluated.

RESULTS

Thirty-four patients (39%) were diagnosed as the homo-HER2 group and 53 patients (61%) were the hetero-HER2 group. After the median follow-up period of 17.8 months, the median PFS and OS were 7.6 and 17.8 months, respectively. Significant survival differences were shown between the two groups; the homo-HER2 group showed significantly longer PFS (10.8 vs. 6.1 months, HR 0.469 95% CI 0.29-0.77, p = 0.003) and OS (29.3 vs. 14.4 months, HR 0.352 95% CI 0.20-0.61, p < 0.001). ORR was 68.6% in this cohort. Higher response rate (85.2% vs 58.1%, p = 0.020) and deeper response (- 49.0% vs - 40.0%, p = 0.018) were also found in the homo-HER2 group.

CONCLUSIONS

Similar to surgical specimens, we verified clinical significance of HER2 heterogeneity on trastuzumab efficacy using endoscopic biopsy specimens.

Clinical relevance of circulating tumor DNA assessed through deep sequencing in patients with metastatic colorectal cancer

Because circulating tumor DNA (ctDNA) studies focusing on only one or a few genes to monitor the disease progress or treatment response are unlikely to find its clinical significance, the development of cell‐free DNA (cfDNA) panel covering hundreds of mutation hot spots is important for the establishment of clinically practical ctDNA detection system. We enrolled 101 patients with metastatic colorectal cancer (mCRC) who received chemotherapy. Amplicon‐based genomic profiling of 14 genes, which are commonly mutated in CRC, in plasma by next‐generation sequencing (NGS) was carried out to evaluate the feasibility of this assay and was compared with their clinical parameters and RAS status in matched tissue samples. Somatic mutations of the 14 genes in plasma cfDNA were detected in 88 patients (87.1%) with mCRC. Mutations in TP53, KRAS, and APC genes were detected in 70 (69.3%), 39 (38.6%), and 24 (23.7%) patients, respectively. Mutant allele frequencies in plasma were significantly associated with metastasis (liver, P = 0.00004, lymph node, P = 0.008, number of metastatic organs, P = 0.0006), tumor markers (CEA, P = 0.000007, CA19‐9, P = 0.006, LDH, P = 0.00001), and tumor diameter (maximum, P = 0.00002, sum of diameter, P = 0.00009). The overall concordance rate of RAS status between ctDNA and matched tissue was 77.2% (78/101). Our data confirmed that mutant allele in cfDNA can be sensitively detected by amplicon‐based NGS system. These results suggest that ctDNA could be a novel diagnostic biomarker to monitor changes in mutational status and tumor burden in patients with mCRC.

Treatment features of systemic chemotherapy in young adults with unresectable advanced or recurrent gastric cancer

Purpose

Gastric cancer in young adults (GCYA) is known to have distinct clinicopathological features, including a female predominance and diffuse-type histology. Previous reports have focused on patients who had undergone gastrectomy with curative intent. Information concerning the treatment of unresectable advanced- or recurrent-stage GCYA is lacking. Therefore, we aimed to investigate whether the distinct clinicopathological features of GCYA affect the outcome of systemic chemotherapy.

Patients and methods

We conducted a retrospective cohort study at a single institution in Japan. GCYA was classified as a disease in individuals who were <40 years of age at diagnosis. Initial systemic chemotherapy regimens for GCYA were investigated with a focus on patients who received S-1 plus cisplatin (SP) as a representative standard regimen. The efficacy, safety, and feasibility of systemic chemotherapy were evaluated.

Results

Eighty-nine (7.5%) of 1,184 consecutive patients who received systemic chemotherapy at our institute between December 2005 and June 2016 were enrolled. As reported previously, the female sex (57.3%) and diffuse-type histology (91.0%) were the dominant features of GCYA. Thirty-two patients (36.0%) received SP as first-line treatment. The median overall survival and progression-free survival times were 13.2 (95.0% CI: 9.5-18.7) and 5.6 (95.0% CI: 4.7-7.9) months, respectively. The median number of treatment cycles, relative dose intensity, and cumulative dose of cisplatin were 4.5 (range: 1-10), 92.0% (IQR: 83.5-98.3), and 286.5 mg/m² (IQR: 172.5-367.5), respectively. The most common adverse event of Grade 3 or higher was neutropenia (n=5 patients; 15.6%). No patient had febrile neutropenia. Non-hematological adverse events of Grade 3 or higher were only observed in 2 (6.3%) of 32 patients.

Conclusion

Standard chemotherapy used for general-aged GC patients has similar efficacy, reduced toxicity, and higher intensity in GCYA patients.

Modified FOLFOX6 as a first-line treatment for patients with advanced gastric cancer with massive ascites or inadequate oral intake

Background

Oral fluoropyrimidine plus platinum is a standard first-line treatment for advanced gastric cancer (AGC). However, this treatment is problematic for AGC patients with massive ascites or inadequate oral intake. This study aimed at evaluating the efficacy and safety of modified oxaliplatin (L-OHP) with l-leucovorin (l-LV) and bolus/continuous infusion of 5-fluorouracil (5-FU) (mFOLFOX6) regimen for patients with massive ascites or inadequate oral intake.

Methods

This retrospective study was conducted at a single Japanese institute from November 2015 to May 2018. The mFOLFOX6 regimen consisted of 85 mg/m² L-OHP, 400 mg/m² bolus of 5-FU, and 400 mg/m² 1-LV on the first day, followed by 2,400 mg/m² of 5-FU as a continuous infusion in 46 hours for first-line treatment. The definition of inadequate oral intake was the need for total parenteral nutrition (TPN). Massive ascites was defined as continuous ascites from the pelvic cavity to the upper abdomen. Improvement in oral intake was defined as no TPN for more than 7 days, and improvement in ascites was defined as a decrease in ascites of more than one grade defined by the Japan Clinical Oncology Study Group trial (JCOG0106).

Results

Among the 364 patients with AGC who received first-line chemotherapy, 17 patients (13 [76.5%] had inadequate oral intake, and four [23.5%] had massive ascites) were enrolled in this study. Median time to treatment failure and overall survival were 4.8 (95% CI=1.5-7.5) and 8.8 months (95% CI=2.3-not available), respectively. Objective improvements in oral intake and ascites were seen in 11 of 13 patients (84.6%) and 6 of 12 patients (50%), respectively. The major grade 3 or 4 adverse events were neutropenia (35.3%), febrile neutropenia (5.9%), fatigue (5.9%), anorexia (5.9%), and infection (5.9%). No treatment-related deaths occurred.

Conclusion

We found that mFOLFOX6 can be a novel treatment option as the first-line treatment for AGC patients with massive ascites or inadequate oral intake.

Clinical impact of intratumoral HER2 heterogeneity on trastuzumab efficacy in patients with HER2-positive gastric cancer

BACKGROUND

There is growing interest in the clinical significance of intratumoral HER2 heterogeneity. Its prognostic and predictive impacts on trastuzumab efficacy were demonstrated in breast cancer. However, its clinical significance in gastric cancer is still unclear.

METHODS

Twenty-eight HER2-positive gastric cancer patients who had gastrectomy prior to trastuzumab-based chemotherapy were consecutively enrolled. Intratumoral HER heterogeneity was evaluated using whole-tissue sections by immunohistochemistry. When all tumor cells overexpressed HER2 protein, the tumor was defined as homogeneously HER2 (Homo-HER2)-positive group. The others were defined as heterogeneously HER2 (Hetero-HER2)-positive group.

RESULTS

There was no significant difference in clinicopathological features between the two groups. The median progression-free survival (PFS) and overall survival (OS) in the Homo-HER2-positive group were significantly longer than those in the Hetero-HER2-positive group (PFS; 20.0 months [95% CI 17.8-22.2] vs. 6.0 months [95% CI 2.3-9.7]; HR 0.11; 95% CI 0.03-0.41; p < 0.001, OS; not reached vs. 14.0 months [95% CI 11.9-16.1]; HR 0.18; 95% CI 0.06-0.61; p = 0.003). In the multivariate analysis, these associations remained significant both in PFS (HR 0.12; 95% CI 0.03-0.46, p = 0.002) and OS (HR 0.21; 95% CI 0.06-0.72, p = 0.013). With respect to response rate, no statistical difference was found between two groups. However, deeper tumor shrinkage was obtained in the Homo-HER2-positive group compared with the Hetero-HER2-positive group (p = 0.046).

CONCLUSIONS

Intratumoral HER2 heterogeneity may have robust clinical impact on trastuzumab efficacy in patients with HER2-positive gastric cancer. These findings should be validated by larger independent cohorts and further molecular correlative analyses are warranted.

Two Cases of Long-Term Survival of Advanced Colorectal Cancer with Synchronous Lung Metastases Treated with mFOLFOX6/XELOX + Bevacizumab

Background

Colorectal cancer (CRC) with lung metastases has an unfavorable prognosis. However, nowadays, even advanced CRC can have a favorable outcome in certain cases. A complete response (CR) is a rare event in advanced CRC with lung metastases. Herein, we report 2 rare cases of advanced CRC attaining a CR.

Case Presentation

Case 1 was a 58-year-old man who underwent laparoscopic ileocecal resection for cecum cancer with multiple metastases to the lungs in 2011. We performed treatment with mFOLFOX6 and bevacizumab chemotherapy in August 2011. After 11 courses, computed tomography (CT) revealed a CR to chemotherapy in February 2012. He has remained disease-free for 5 years and 3 months. Case 2 was a 70-year-old woman who underwent laparoscopic ileocecal resection for cecum cancer in August 2010. Recurrence of multiple metastases to both lungs was detected in November 2010. We started treatment with XELOX and bevacizumab chemotherapy in January 2011. In January 2011, CT after 14 courses revealed disappearance of the lung lesions, thereby indicating a CR. She has remained disease-free for 5 years and 4 months.

Conclusion

We encountered 2 patients with CRC with lung metastases who were treated with chemotherapy leading to a CR. Cases resulting in such a desirable outcome are extremely rare.

Abstract 4580: Changes in the efficacy of anti-EGFR antibody drugs by exosomes derived from colorectal cancer patients

Background: One of the biggest hurdles in cancer treatment is drug resistance. Exosomes are small membrane vesicles of endocytic origin, which contain mRNAs, DNA fragments, and proteins, and are released by many different cell types, including cancer cells. Several studies have shown exosome-mediated drug resistance mechanisms: drug export via the exosome pathway, neutralization of antibody-based drugs and exosome-mediated transfer of miRNAs. Here, we demonstrated the effect of exosomes derived from colorectal cancer (CRC) patients on the efficacy of anti-EGFR agent by in vitro cell-based assay.

Method: Exosomes were purified by ultracentrifugation from culture media of HCT116 cell line and the sera of CRC patients with stage IV pre- and post-treatment with cetuximab (Cmab). As a control, sera from healthy volunteers were used. The number of exosomes and amount of protein were determined by NanoSight and Qubit fluorometer, respectively. The isolated exosomes and 0.01 mg/mL and 0.1 mg/mL of Cmab were added to HT29 and NCI-H508, which stained with PKH dye previously. NCI-H508 is a Cmab super sensitive cell line. After culturing for 3 days, the cells were collected, stained with trypan blue, and the number of the remaining viable cancer cells was calculated with a cell counter. Cmab in the exosome fraction was quantified by ELISA.

Result: HT29 became drug ineffective depending on the number of exosomes produced by Cmab-insensitive HCT-116 harboring KRAS G13D mutation. In addition, exosomes in 9 of 18 cases of colorectal cancer patients changed NCI-H508 into a drug-ineffective state and also correlated with clinical information. In contrast, NCI-H508 was not converted into a drug-ineffective state by exosomes of healthy volunteers and Cmab responder patients. However, on the other hand, quantitative results by ELISA showed that Cmab in sera of some patients remained in the exosome fraction and inhibited the growth of NCI-H508. As a remarkable point, exosomes derived from healthy volunteers significantly promoted the efficacy of Cmab.

Conclusion: In this feasibility study, Cmab resistance in CRC patients may be reproducible by cell-based assay using exosomes. We believe that understanding this mechanism of action will contribute to drug discovery and personalized medicine in the future. Now, we are searching for biomarkers in these exosomes that change the efficacy of Cmab.

Citation Format: Rii Morimura, Kei Tsukamoto, Shinji Irie, Shiro Kitano, Eiji Shinozaki, Kensei Yamaguchi. Changes in the efficacy of anti-EGFR antibody drugs by exosomes derived from colorectal cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4580.

Abstract 5016: A unique ex vivo drug evaluation model: 3D co-cultured system with tumor, stroma and blood microvessels

Background; Two dimensional single-layer culture still remains the preferred platform for most laboratory preclinical studies, although interaction between cancer and stromal cells has been well reported to be important in tumor progression and resistance against therapies. In order to mimic the patient tumor tissues, ex vivo model which recaptures the tumor microenvironment is required.

Methods; Layered 3D stromal tissues were produced by culturing normal human dermal fibroblasts (NHDFs) and human umbilical vein endothelial cells (HUVECs) coated with extra-cellular matrix (ECM) and natural polysaccharide, namely collagen and heparin. The layered 3D stromal tissues and overlaid tumors were morphologically characterized by HE stain, immunohistochemistry (IHC) and immunofluorescence (IF). Furthermore, drug sensitivity assays were conducted using popular colorectal cancer cell lines, and patient-derived cell lines (PDCs) established in the laboratory of Japanese Foundation for Cancer Research. Cancer cell viability was evaluated by fluorescent labeling, enzymatic dissociation and cell counting analysis. IF with cancer specific markers and imaging analyses were also performed.

Results; The 3D stromal tissues including CD31 positive luminal structure were multi-layered (approximately 20 layers), and formation of microvascular network was observed within several days. In comparison with 2D mono-culture or 3D mono/co-cultured spheroid model, decreased drug sensitivities were represented in our 3D co-cultured model. In the simultaneous treatment with cytotoxic anticancer agents and molecular targeted drugs, dose-responses were significantly different between the2D and 3D models.

Conclusion; We developed the layered 3D stromal tissue culture system including blood micro-vessels. Drug evaluation with the co-cultured tumors may reflect the drug sensitivity of cancer cells in vivo. Our unique 3D ex vivo model represents a valuable tool for drug development in a fully human cell and matrix microenvironment, and thus testing patient-derived cells and approved compounds also enable better prediction their efficacy.

Citation Format: Yuki Takahashi, Kei Tsukamoto, Shiro Kitano, Shinji Irie, Michiya Matsusaki, Satoshi Nagayama, Ryohei Katayama, Eiji Shinozaki, Naoya Fujita. A unique ex vivo drug evaluation model: 3D co-cultured system with tumor, stroma and blood microvessels [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5016.

Abstract 1151: A unique layered 3D stromal tissue model for in vitro evaluation of immunologic agents and immune cell infiltration into cancer microenvironment

Background; The modulation of the immune system is a proven key target for cancer therapy, however, the complex interplay between immune cells and cancer cells in cancer microenvironment remains only partially understood. In addition, the currently available in vitro cancer microenvironment models are not designed to study the immunologic agents and a role of immune cells. Here, we developed a unique layered 3D stromal tissue model comprising an allogeneic immune, stromal and cancer cells.

Method; Human umbilical vein endothelial cells (HUVEC) and normal human dermal fibroblasts (NHDF) were coated with collagen and heparin to construct Extracellular matrix (ECM) nanofilm and cultured to form multi-layers. Lung cancer cells were placed between stromal cells. Furthermore, we added Peripheral Blood Mononuclear Cell (PBMC) and Programmed cell death 1 (PD-1) blockade with Nivolumab and evaluated cytotoxic effects of immune cells on cancer cells and immune cell infiltration by immunohistochemistry.

Result; The co-cultured stromal tissues were multi-layered (approximately 20 layers), and the presence of lung cancer cells between stromal cells was observed. Immunohistochemistry revealed CD8 positive immune cell infiltration into the fibroblast layers. PBMC with Nivolumab treatment significantly decreased the viability of lung cancer cells in this 3D co-culture compared with the results in 2D mono-culture. High level of programmed cell death ligand 1 (PD-L1) expression on lung cancer cell lines correlated with a higher response to PD-1 blockade in vitro as well as clinical trials.

Conclusion; In summary, we present a unique 3D cell culture system based on an allogeneic stromal/cancer/immune cell setting to study immunologic agents and immune cell infiltration in cancer microenvironment. This 3D model has the ability to reflect in vivo conditions closer than 2D model and provide a tool for in vitro immunologic agent testing.

Citation Format: Rii Morimura, Kei Tsukamoto, Shiro Kitano, Eiji Shinozaki. A unique layered 3D stromal tissue model for in vitro evaluation of immunologic agents and immune cell infiltration into cancer microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1151.

Abstract 2962: Clinical relevance of circulating cell-free DNA using amplicon-based next-generation sequencing panel in colorectal cancer patients with liver metastasis

Background: Recent advances in the next-generation sequencing technique (NGS) for the detection of cell-free DNA (cfDNA) will be possible to provide the utility as diagnostic and prognostic biomarkers of cancer. We conducted the study of feasibility to detect plasma cfDNA from patients with metastatic colorectal cancer (mCRC) using NGS panel and investigated their relationship with clinicopathological factors.

Methods: A total of 101 mCRC patients with liver metastasis, who had been treated with chemotherapy, were enrolled in this study from February to June in 2017. We investigated i) frequency of detectable mutations in plasma cfDNA, ii) concordance rate of RAS mutation between the DNA extracted from tissues and the plasma cfDNA, iii) relationship between the mutation allele frequencies (MAF) and clinicopathological factors including tumor location, metastatic site, number of metastatic organs, tumor marker (CEA and CA19-9), LDH level, D-dimer level and sum of the tumor diameter measured based on RECIST ver1.1 criteria. Sequencing of plasma cfDNA were performed using Ion Torrent™ Oncomine™ Colon cfDNA Assay.

Results: Mutations in plasma cfDNA were detected in 87.1% (88/101) of patients. The frequencies of plasma cfDNA mutation at TP53, KRAS, APC, and PIK3CA were 68.3%, 38.6%, 23.7%, and 14.8%, respectively. RAS mutational concordance rate between DNA extracted from tumor and cfDNA was 76.2% (77/101). MAF were significantly associated with CEA (P&lt;0.0001), CA19-9 (P=0.006), LDH (P&lt;0.0001) and number of metastatic organs (P&lt;0.0001). Patients with liver or lymph node metastasis had significantly higher MAF compared with those without metastases (Liver: P&lt;0.0001, Lymph node: P=0.008). Positive correlations between CEA level, CA19-9 level, LDH level, tumor diameter and MAF were observed. (CEA: r=0.52, CA19-9: r=0.34, LDH: r=0.55, tumor diameter: r=0.57)

Conclusions: Our results suggested that this cfDNA Assays could detect mutations at a high rate of mCRC patients undergoing chemotherapy and cfDNA analysis using NGS panel could be useful method of diagnostic biomarkers to monitor the change of RAS status and tumor burden. &lt;!–EndFragment–&gt;

Citation Format: Hiroki Osumi, Eiji Shinozaki, Hitoshi Zembutsu, Yoshinori Takeda, Takeru Wakatsuki, Takashi Ichimura, Yumiko Ota, Izuma Nakayama, Mariko Ogura, Mitsukuni Suenaga, Daisuke Takahari, Keisho Chin, Akio Saiura, Kensei Yamaguchi. Clinical relevance of circulating cell-free DNA using amplicon-based next-generation sequencing panel in colorectal cancer patients with liver metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2962.

Abstract 1954: Functional analyses of CLDN18-ARHGAP26 fusion gene in gastric cancers

[Introduction]Comprehensive molecular analyses by TCGA have classified Gastric Cancers (GC) into 4 groups: EB virus -associated (EBV), Microsatellite instability (MSI), Genomically stable (GS) and Chromosomal instability (CIN). Among these 4 subtypes, patients with GS subtype have few actionable genetic alterations and thus a limited number of molecular-targeted treatments are available. A fusion gene between CLDN18 and ARHGAP26 was first reported by TCGA to be enriched in GS subtype (13.8%), but the prospective functions of this gene product remain unknown.

[Methods]We have previously established 124 GC-Patient derived xenografts (PDXs) from surgically resected specimens in our institute. There are various types of GCs in the PDX panel, including intestinal and diffuse type tumors or tumors of primary and metastatic site. In an attempt to assess roles of CLDN18-ARHGAP26 fusion gene in gastric cancers, we used the cultured cells obtained from GC-PDXs. We first prepared tissue micro-array of formalin-fixed and paraffin-embedded (FFPE) specimen of PDXs and screened for the patients harboring a CLDN18-ARHGAP26 fusion genes by FISH and RT-PCR. In addition, fusion positive cases were sequenced to determine the breakpoints by direct sequencing. Then, we conducted several functional analyses, including assays for cellular proliferation and mobility, by RNAi-knockdown experiments.

[Results]Among 124 GC-PDXs, we detected two CLDN18-ARHGAP26 fusion positive cases. Both of these 2 cases were derived from tumors with diffuse-type GC patient and had identical breakpoint between CLDN18 (exon 5) and ARHGAP26 (exon 10). We successfully established cell lines of these 2 cases. Furthermore, we would verify that PDX derived cells preserved the original patient properties, as transplantation of the PDX-derived cells histologically recapitulated the original tumors. To address its function, we introduced siRNA into cultured cells to reduce their protein levels. Our data so far indicate that the CLDN18-ARHGAP26 fusion might promote anchorage independent cell growth.

[Conclusion] The CLDN18-ARHGAP26 fusion gene potentially contributes to malignant phenotypes of GC. Further analyses in vivo are awaited.

Citation Format: Izuma Nakayama, Eiji Shinozaki, Tetsuo Mashima, Tokuichi Kawaguchi, Seiji Sakata, Noriko Yamamoto, Satoko Baba, Akito Dobashi, Yuki Togashi, Minoru Sugawara, Shunji Takahashi, Kensei Yamaguchi, Kengo Takeuchi, Tetsuo Noda. Functional analyses of CLDN18-ARHGAP26 fusion gene in gastric cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1954.

Phase II trial of biweekly cetuximab and irinotecan as third-line therapy for pretreated KRAS exon 2 wild-type colorectal cancer

Efficacy and safety of biweekly cetuximab plus irinotecan were evaluated to provide guidance for its use in Japan as third-line treatment for pretreated metastatic colorectal cancer (mCRC) patients harboring wild-type KRAS exon 2. Objective response rate (ORR) was used as primary endpoint based on an expected proportion of 0.23 with confidence width of 0.298 (95% CI, 0.105-0.403), which showed 35 to be the minimal participant number. Forty patients, refractory to first- and second-line chemotherapy containing irinotecan, oxaliplatin, and fluoropyrimidine, were enrolled. ORR and disease control rate were 25.0% (95% CI: 11.5-38.4) and 72.5% (95% CI: 56.8-86.4), respectively. Median progression-free survival (PFS), overall survival (OS), and number of courses were 5.70 months (95% CI: 2.7-7.9), 15.1 months (95% CI: 11.8-19.0), and 10.5 (range: 3.0-31.0), respectively. Grade 3 adverse events were skin toxicity (12.5%), diarrhea (10.0%), neutropenia (5.0%), febrile neutropenia (5.0%), nausea (5.0%), anorexia (5.0%), and fatigue (2.5%). C_max mean was 723.2 μg/mL after first dose. High area under the curve (AUC)_last variance was associated with t_1/2 range of 131.2-1209.6 hours (median, 174.4 hours). Early tumor shrinkage (ETS) and median depth of response were 25.0% and 13.0%, respectively. Mutation frequencies in KRAS exon 3 or 4, NRAS, BRAF, and PIK3CA were 5.5%, 2.7%, 8.3%, and 5.5%, respectively. Multivariate Cox regression analysis assessed whether any gene mutations and ETS are predictors for PFS, and whether performance status, synchronous metastasis, and ETS are predictors for OS. Importantly, the data provide guidance for a biweekly cetuximab plus irinotecan regimen in mCRC patients.

Serum leucine-rich alpha-2-glycoprotein-1 with fucosylated triantennary N-glycan: a novel colorectal cancer marker

BACKGROUND

Carcinoembryonic antigen (CEA) and carbohydrate antigen (CA)19-9 are used in clinical practice as tumor markers to diagnose or monitor colorectal cancer (CRC) patients, However, their specificities and sensitivities are not ideal, and novel alternatives are needed. In this study, mass spectrometry was used to search for screening markers, focusing on glycan alterations of glycoproteins in the sera of CRC patients.

METHODS

Glycopeptides were prepared from serum glycoproteins separated from blood samples of 80 CRC patients and 50 healthy volunteers, and their levels were measured by liquid chromatography time-of flight mass spectrometry (LC-TOF-MS).

RESULTS

Leucine-rich alpha-2-glycoprotein-1 with fucosylated triantennary N-glycan (LRG-FTG) was identified as CRC marker after evaluating 30,000 candidate glycopeptide peaks. The average LRG-FTG level in CRC patients (1.25 ± 0.973 U/mL) was much higher than that in healthy volunteers (0.496 ± 0.433 U/mL, P < 10^- 10), and its sensitivity and specificity exceeded those of CA19-9. The combination of CEA and LRG-FTG showed a complementary effect and had better sensitivity (84%), specificity (90%), and AUC (0.91 by ROC analysis) than each marker alone or any other previously reported marker. LRG-FTG alone or combined with CEA also corresponded well with patient response to treatment.

CONCLUSIONS

We identified LRG-FTG as a new CRC marker, with a sensitivity and specificity exceeding CA19-9. The combination of LRG-FTG and CEA showed much higher sensitivity and specificity than each marker alone. Further validation beyond this initial exploratory cohort is warranted.