Impact of Mutations in Subunit Genes of the Mammalian SWI/SNF Complex on Immunological Tumor Microenvironment

BACKGROUND/AIM

Recently, inactivating somatic mutations of SWI/SNF chromatin-remodeling genes in cancers have been reported. However, few studies have been performed regarding the immunological analysis of the tumor microenvironment (TME) in chromatin remodeling complex gene-mutated tumors. In the present study, we identified cancer patients harboring various mammalian SWI/SNF complex mutations and investigated the immunological features in those mutated cancers.

PATIENTS AND METHODS

Cancer patients harboring any type of chromatin remodeling complex gene mutation were selected and clinicopathological features were compared between chromatin remodeling complex gene expression-low and expression-high groups. Specifically, expression levels of immune response-associated genes and cancer-associated genes were compared between the SMARCA4 expression-low and expression-high groups using volcano plot analysis.

RESULTS

Among cancers harboring PBRM1, SAMRACA4 and ARID2 gene mutations, T-cell marker and mature B-cell marker genes were up-regulated in the tumor. Specifically, T-cell effector genes (CD8B, CD40LG), central memory marker genes (CD27, CCR7) and mature B-cell marker genes (CD20, CD38, CD79 and IRF4) were up-regulated, and cancer-associated genes including MYB, MYC and AURKB genes were down-regulated in the SMARCA4 expression-low group. Remarkably, heatmap of gene expression and immunohistochemistry (IHC) data demonstrated that the tertiary lymphoid structure (TLS) gene signature of mature B cells was up-regulated in SMACA4 gene-mutated stomach cancers.

CONCLUSION

These results suggest that immune tumor microenvironment status, such as mature B cell recruitment featuring the TLS gene signature and immune activation mediated by cancer signal down-regulation, might contribute to the classification of SMARCA4 gene-mutated tumors as immune checkpoint blockade therapy-sensitive target tumors.

Localization of EGFR Mutations in Non-small-cell Lung Cancer Tissues Using Mutation-specific PNA-DNA Probes

BACKGROUND/AIM

Epidermal growth factor receptor (EGFR) signaling inhibitors are potent therapeutic agents for EGFR-mutant non-small-cell lung cancer, but the effects of such inhibitors on the localization of EGFR mutations in tumor tissues remain to be elucidated. Thus, a simple and efficient technology for the detection of mutations in tumor tissue specimens needs to be developed.

MATERIALS AND METHODS

Using an EGFR mutation-specific peptide nucleic acid (PNA)-DNA probe, the EGFR mutation-positive part of whole NSCLC tissues was visualized by immunofluorescence. Formalin-fixed paraffin-embedded sections obtained from A549, NCI-H1975, HCC827 and PC-9 tumors transplanted into nude mice were subjected to staining using PNA-DNA probes specific for the mRNA sequences producing the L858R, del E746-A750 and T790M mutations.

RESULTS

The probes for the L858R mutation showed intense positive staining in H1975 cells, and the probe for the del E746-A750 mutation exhibited positive staining specifically in HCC827 and PC-9 tumors. On the other hand, A549 tumors without EGFR mutation did not show any significant staining for any PNA-DNA probe. In combination staining, the addition of cytokeratin stain increased the positive staining rate of each PNA-DNA probe. In addition, the positive staining rate of the probes for the L858R mutation was comparable to that of the antibody to EGFR L858R mutated protein.

CONCLUSION

PNA-DNA probes specific for EGFR mutations might be useful tools to detect heterogeneous mutant EGFR expression in cancer tissues and efficiently evaluate the effect of EGFR signaling inhibitors on tissues of EGFR-mutant cancer.

Characterization of the Immunological Status of Hypermutated Solid Tumors in the Cancer Genome Analysis Project HOPE

BACKGROUND

Many reports demonstrate that a high tumor mutation burden (TMB-H) is closely associated with good prognosis of cancer. However, specific studies investigating the association of various TMB statuses with overall survival in patients with solid tumors are scarce.

PATIENTS AND METHODS

In the present study, we investigated the association of TMB status with overall survival in 5,072 patients with cancer from the HOPE project and clarified the specific mechanism responsible for the good prognosis of the TMB-H group. All tumors were classified into one of four groups based on TMB: ultralow (UL), low (L), intermediate (I) and high (H).

RESULTS

The TMB-H group had a better prognosis than the TMB-I and TMB-L groups, but not than the TMB-UL group. Analyzing the expression of 293 immune response-associated genes, 17 genes were up-regulated in the TMB-H group compared to the TMB-I and TNB-L groups, and two genes [CD274 and interferon-γ (IFNG)] were identified as good prognostic factors. Analysis of immune cell populations inside tumors demonstrated that the frequencies of exhausted CD8⁺ T-cells, activated effector CD8⁺ T-cells and natural killer cells were significantly higher in the TMB-H group. The T-cell receptor repertoire numbers and the diversity evenness score (DE50) were lower in the TMB-H group than in TMB-UL group; however, no association of the DE50 value with the binding or elution affinity of epitope peptides from neoantigens was found.

CONCLUSION

One possible mechanism for the good prognosis of the TMB-UL group compared to the TMB-H group might be that the TMB-UL group features a balance between immunosuppression and immunostimulation.

Development of an Automatic Measurement Method for CD8 and PD-1 Positive T Cells Using Image Analysis Software

BACKGROUND/AIM

With the progress in cancer immunotherapy using immune checkpoint blockade (ICB) therapy, histological observations of tumor-infiltrating lymphocyte (TIL) status are needed to evaluate the antitumor effect of ICB using imaging analysis software.

MATERIALS AND METHODS

Formalin-fixed paraffin-embedded sections obtained from colorectal cancer and gastric cancer patients with more than 500 single nucleotide variants were stained with anti-CD8 and anti-PD-1 antibodies. Based on our own algorithm and imaging analysis software, an automatic TIL measurement method was established and compared to the manual counting methods.

RESULTS

In the CD8⁺ T cell number measurement, there was a good correlation (r=0.738 by Pearson test) between the manual and automated counting methods. However, in the PD-1⁺ T cell measurement, there was a large difference in TIL numbers in both groups. After adjustment of the parameter settings, the correlation between the manual and automated methods in the PD-1⁺ T cell measurements improved (r=0.668 by Pearson test).

CONCLUSION

An imaging software-based automatic measurement could be a simple and useful tool for evaluating the therapeutic effect of cancer immunotherapies in terms of TIL status.

Identification of tumor microenvironment-associated immunological genes as potent prognostic markers in the cancer genome analysis project HOPE

Project High-tech Omics-based Patient Evaluation (HOPE), which used whole-exome sequencing and gene expression profiling, was launched in 2014. A total of ~2,000 patients were enrolled until March 2016, and the survival time was observed up to July 2019. In our previous study, a tumor microenvironment immune type classification based on the expression levels of the programmed death-ligand 1 (PD-L1) and CD8B genes was performed based on four types: A, adaptive immune resistance; B, intrinsic induction; C, immunological ignorance; and D, tolerance. Type A (PD-L1⁺ and CD8B⁺) exhibited upregulated features of T helper 1 antitumor responses. In the present study, survival time analysis at 5 years revealed that patients in type A had a better prognosis than those in other categories [5 year survival rate (%); A (80.5) vs. B (73.9), C (73.4) and D (72.6), P=0.0005]. Based on the expression data of 293 immune response-associated genes, 62 specific genes were upregulated in the type A group. Among these genes, 18 specific genes, such as activated effector T-cell markers (CD8/CD40LG/GZMB), effector memory T-cell markers (PD-1/CD27/ICOS), chemokine markers (CXCL9/CXCL10) and activated dendritic cell markers (CD80/CD274/SLAMF1), were significantly associated with a good prognosis using overall survival time analysis. Finally, multivariate Cox proportional hazard regression analyses of overall survival demonstrated that four genes (GZMB, HAVCR2, CXCL9 and CD40LG) were independent prognostic markers, and GZMB, CXCL9 and CD40LG may contribute to the survival benefit of patients in the immune type A group.

Outcomes of robot-assisted versus conventional laparoscopic low anterior resection in patients with rectal cancer: propensity-matched analysis of the National Clinical Database in Japan

BACKGROUND

Robot-assisted laparoscopic surgery has several advantages over conventional laparoscopy. However, population-based comparative studies for low anterior resection are limited. This article aimed to compare peri-operative results of robot-assisted low anterior resection (RALAR) and laparoscopy.

METHODS

This retrospective cohort study used data from patients treated with RALAR or conventional laparoscopic low anterior resection (CLLAR) between October 2018 and December 2019, as recorded in the Japanese National Clinical Database, a data set registering clinical information, perioperative outcomes, and mortality. Of note, the registry does not include information on the tumour location (centimetres from the anal verge) and diverting stoma creation. Perioperative outcomes, including rate of conversion to open surgery, were compared between RALAR and CLLAR groups. Confounding factors were adjusted for using propensity score matching.

RESULTS

Of 21 415 patients treated during the study interval, 20 220 were reviewed. Two homogeneous groups of 2843 patients were created by propensity score matching. The conversion rate to open surgery was significantly lower in the RALAR group than in the CLLAR group (0.7 versus 2.0 per cent; P < 0.001). The RALAR group had a longer operating time (median: 352 versus 283 min; P < 0.001), less intraoperative blood loss (15 versus 20 ml; P < 0.001), a lower in-hospital mortality rate (0.1 versus 0.5 per cent; P = 0.007), and a shorter postoperative hospital stay (median: 13 versus 14 days; P < 0.001) compared with the CLLAR group. The CLLAR group had a lower rate of readmission within 30 days (2.4 versus 3.3 per cent; P = 0.045).

CONCLUSION

These data highlight the reduced conversion rate, in-hospital mortality rate, intraoperative blood loss, and length of postoperative hospital stay for rectal cancer surgery in patients treated using robot-assisted laparoscopic surgery compared with laparoscopic low anterior resection.

Alternative Evaluation of an ELISPOT Assay Using Cytokine Activity as a Novel Parameter

BACKGROUND/AIM

The enzyme-linked immunospot (ELISPOT) assay is a well-established method used to evaluate the strength of T cell-mediated immune activity, and accepted as a standard functional immunological assay. Cytokine activity is a novel parameter reflecting spot size and intensity, which has not been used in ELISPOT assay before.

MATERIALS AND METHODS

In the present study, from 113 ELISPOT assay data derived from previous clinical trials with dendritic cell vaccines, both spot number count and cytokine activity data for IFN-γ secretion were obtained using an ELISPOT reader. Comparing the new parameter cytokine activity with the existing parameter spot number, the feasibility of cytokine activity was investigated.

RESULTS

There were no significant differences in sensitivity and specificity between spot number and cytokine activity among ELISPOT assay data from CMVpp65 and other antigen peptide-stimulated cytotoxic T lymphocytes.

CONCLUSION

Although cytokine activity is a novel parameter unreported so far, it did not show any advantages in the evaluation T cell immune responses compared to the existing spot number parameter.

Test of Lepton-Flavor Universality in B→K^{*}ℓ^{+}ℓ^{-} Decays at Belle

We present a measurement of R_{K^{*}}, the branching fraction ratio B(B→K^{*}μ^{+}μ^{-})/B(B→K^{*}e^{+}e^{-}), for both charged and neutral B mesons. The ratio for the charged case R_{K^{*+}} is the first measurement ever performed. In addition, we report absolute branching fractions for the individual modes in bins of the squared dilepton invariant mass q^{2}. The analysis is based on a data sample of 711  fb^{-1}, containing 772×10^{6}  BB[over ¯] events, recorded at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The obtained results are consistent with standard model expectations.

Safety and feasibility of laparoscopic surgery for elderly rectal cancer patients in Japan: a nationwide study

Background

This study aimed to analyse the perioperative results from a national dataset of rectal cancer resections in elderly patients.

Methods

The clinical records of patients undergoing rectal cancer surgery between 2012 and 2014 were retrieved from the Japanese National Clinical Database and analysed retrospectively. Patients were categorized according to age and those 80 years or older were defined as elderly. Subgroups were also defined according to the surgical approach (laparoscopy versus open surgery). The short-term outcomes, including mortality, anastomotic leak, surgical site infections and medical complications were compared between subgroups.

Results

Of 56 175 patients undergoing rectal cancer surgery, some 6717 patients were elderly and laparoscopy was performed in 46.8 per cent of the sample. When comparing laparoscopy and open surgery in elderly patients, the operative mortality rate (1.5 versus 2.8 per cent; P < 0.001), the incidence of anastomotic leakage (5.2 versus 6.5 per cent; P = 0.026), surgical site infections (6.0 versus 8.0 per cent; P = 0.001), pneumonia (1.4 versus 2.5 per cent; P = 0.001), renal failure (0.7 versus 1.3 per cent; P = 0.016) and cardiac events (0.3 versus 0.8 per cent; P = 0.008) were lower for laparoscopy than for open surgery. The overall complication rate in elderly patients (19.5 per cent) was comparable to that in the younger group (P = 0.07). However, incidence of systemic complications was significantly higher in elderly than in younger patients (all P < 0.001).

Conclusion

Laparoscopy was safe and feasible in elderly patients compared with open surgery. However, the rates of systemic complications were significantly higher than in younger patients.

Nationwide study of surgery for primary infected abdominal aortic and common iliac artery aneurysms

BACKGROUND

Primary infected aneurysms of the abdominal aorta and iliac arteries are potentially life-threatening. However, because of the rarity of the disease, its pathogenesis and optimal treatment strategy remain poorly defined.

METHODS

A nationwide retrospective cohort study investigated patients who underwent surgical treatment for a primary infected abdominal aortic and/or common iliac artery (CIA) aneurysm between 2011 and 2017 using a Japanese clinical registry. The study evaluated the relationships between preoperative factors and postoperative outcomes including 90-day and 3-year mortality, and persistent or recurrent aneurysm-related infection. Propensity score matching was used to compare survival between patients who underwent in situ prosthetic grafting and those who had endovascular aneurysm repair (EVAR).

RESULTS

Some 862 patients were included in the analysis. Preceding infection was identified in 30.2 per cent of the patients. The median duration of postoperative follow-up was 639 days. Cumulative overall survival rates at 30 days, 90 days, 1 year, 3 years and 5 years were 94.0, 89.7, 82.6, 74.9 and 68.5 per cent respectively. Age, preoperative shock and hypoalbuminaemia were independently associated with short-term and late mortality. Compared with open repair, EVAR was more closely associated with persistent or recurrent aneurysm-related infection (odds ratio 2.76, 95 per cent c.i. 1.67 to 4.58; P < 0.001). Propensity score-matched analyses demonstrated no significant differences between EVAR and in situ graft replacement in terms of 3-year all-cause and aorta-related mortality rates (P = 0.093 and P =0.472 respectively).

CONCLUSION

In patients undergoing surgical intervention for primary infected abdominal aortic and CIA aneursyms, postoperative survival rates were encouraging. Eradication of infection following EVAR appeared less likely than with open repair, but survival rates were similar in matched patients between EVAR and in situ graft replacement.

Evidence for X(3872)→J/ψπ^{+}π^{-} Produced in Single-Tag Two-Photon Interactions

We report the first evidence for X(3872) production in two-photon interactions by tagging either the electron or the positron in the final state, exploring the highly virtual photon region. The search is performed in e^{+}e^{-}→e^{+}e^{-}J/ψπ^{+}π^{-}, using 825  fb^{-1} of data collected by the Belle detector operated at the KEKB e^{+}e^{-} collider. We observe three X(3872) candidates, where the expected background is 0.11±0.10 events, with a significance of 3.2σ. We obtain an estimated value for Γ[over ˜]_{γγ}B(X(3872)→J/ψπ^{+}π^{-}) assuming the Q^{2} dependence predicted by a cc[over ¯] meson model, where -Q^{2} is the invariant mass squared of the virtual photon. No X(3915)→J/ψπ^{+}π^{-} candidates are found.

Risk prediction model for early outcomes of revascularization for chronic limb-threatening ischaemia

BACKGROUND

Quantifying the risks and benefits of revascularization for chronic limb-threatening ischaemia (CLTI) is important. The aim of this study was to create a risk prediction model for treatment outcomes 30 days after revascularization in patients with CLTI.

METHODS

Consecutive patients with CLTI who had undergone revascularization between 2013 and 2016 were collected from the JAPAN Critical Limb Ischemia Database (JCLIMB). The cohort was divided into a development and a validation cohort. In the development cohort, multivariable risk models were constructed to predict major amputation and/or death and major adverse limb events using least absolute shrinkage and selection operator logistic regression. This developed model was applied to the validation cohort and its performance was evaluated using c-statistic and calibration plots.

RESULTS

Some 2906 patients were included in the analysis. The major amputation and/or mortality rate within 30 days of arterial reconstruction was 5.0 per cent (144 of 2906), and strong predictors were abnormal white blood cell count, emergency procedure, congestive heart failure, body temperature of 38°C or above, and hemodialysis. Conversely, moderate, low or no risk in the Geriatric Nutritional Risk Index (GNRI) and ambulatory status were associated with improved results. The c-statistic value was 0.82 with high prediction accuracy. The rate of major adverse limb events was 6.4 per cent (185 of 2906), and strong predictors were abnormal white blood cell count and body temperature of 38°C or above. Moderate, low or no risk in the GNRI, and age greater than 84 years were associated with improved results. The c-statistic value was 0.79, with high prediction accuracy.

CONCLUSION

This risk prediction model can help in deciding on the treatment strategy in patients with CLTI and serve as an index for evaluating the quality of each medical facility.

Alpha-type-1 Polarized Dendritic Cell-based Vaccination in Newly Diagnosed High-grade Glioma: A Phase II Clinical Trial

BACKGROUND/AIM

Glioblastoma multiforme (GBM) is an intractable tumor that has a very poor prognosis despite intensive treatment with temozolomide plus radiotherapy.

PATIENTS AND METHODS

Sixteen newly diagnosed patients with high-grade gliomas were enrolled in a phase II study of the α-type-1 DC vaccine. Briefly, DCs obtained from the culture of enriched monocytes in the presence of a cytokine cocktail, were pulsed with a cocktail of 5 synthetic peptides and cryopreserved until injection into patients.

RESULTS

The amount of IL-12 produced by activated DCs was higher than that previously reported. Among 15 evaluable patients, 10 showed positive CTL responses to any peptides in an ELISPOT assay. After 6 years of observation, five patients were still alive, and two of these patients were relapse-free. Moreover, a significant survival-prolonging effect was verified in DC-treated glioma patients.

CONCLUSION

Peptide-cocktail-pulsed α-type-1 DC vaccines have a potential therapeutic effect on survival when used in combination with the standard regimen, which is partly based on IL-12-IFN-γ-mediated T-cell activation.

Trend change of the transmission route of COVID-19-related symptoms in Japan

OBJECTIVES

The Japanese prime minister declared a state of emergency on April 7 2020 to combat the outbreak of coronavirus disease 2019 (COVID-19). This declaration was unique in the sense that it was essentially driven by the voluntary restraint of the residents. We examined the change of the infection route by investigating contact experiences with COVID-19-positive cases.

STUDY DESIGN

This study is a population-level questionnaire-based study using a social networking service (SNS).

METHODS

To assess the impact of the declaration, this study used population-level questionnaire data collected from an SNS with 121,375 respondents (between March 27 and May 5) to assess the change in transmission routes over the study period, which was measured by investigating the association between COVID-19-related symptoms and (self-reported) contact with COVID-19-infected individuals.

RESULTS

The results of this study show that the declaration prevented infections in the workplace, but increased domestic infections as people stayed at home. However, after April 24, workplace infections started to increase again, driven by the increase in community-acquired infections.

CONCLUSIONS

While careful interpretation is necessary because our data are self-reported from voluntary SNS users, these findings indicate the impact of the declaration on the change in transmission routes of COVID-19 over time in Japan.

Effect of preoperative chemoradiotherapy on the immunological status of rectal cancer patients

The aim of the study was to investigate the effect of chemo-radiation on the genetic and immunological status of rectal cancer patients who were treated with preoperative chemoradiotherapy (CRT). The expression of immune response-associated genes was compared between rectal cancer patients treated (n = 9) and not-treated (n = 10) with preoperative CRT using volcano plot analysis. Apoptosis and epithelial-to-mesenchymal transition (EMT) marker genes were analysed by quantitative PCR (qPCR). Other markers associated with the tumor microenvironment (TME), such as tumor-infiltrating lymphocytes (TIL) and immune checkpoint molecules, were investigated using immunohistochemistry (IHC). The clinical responses of preoperative CRT for 9 rectal cancer patients were all rated as stable disease, while the pathological tumor regression score (TRG) revealed 6 cases of grade2 and 3 cases of grade1. According to the genetic signature of colon cancers, treated tumors belonged to consensus molecular subtype (CMS)4, while not-treated tumors had signatures of CMS2 or 3. CRT-treated tumors showed significant upregulation of EMT-associated genes, such as CDH2, TGF-beta and FGF, and cancer stem cell-associated genes. Additionally, qPCR and IHC demonstrated a suppressive immunological status derived from the upregulation of inflammatory cytokines (IL-6, IL-10 and TGF-beta) and immune checkpoint genes (B7-H3 and B7-H5) and from M2-type macrophage accumulation in the tumor. The induction of EMT and immune-suppressive status in the tumor after strong CRT treatment urges the development of a novel combined therapy that restores immune-suppression and inhibits EMT, ultimately leading to distant metastasis control.

The relationship between fever rate and telework implementation as a social distancing measure against the COVID-19 pandemic in Japan

Objectives

On March 28, the Japanese government decided on the “Basic Policies for Novel Coronavirus Disease Control” and called on the public to thoroughly implement social distancing measures (i.e., behavioral restrictions to limit the frequency and intensity of human contact), especially telework.

Methods

We used population-level questionnaire data from a social networking service (SNS), with 275,560 respondents from March 5 to April 6, to evaluate the relationship between telework implementation and the presence of a fever (body temperature higher than 37.5 °C) within 1 month as a surrogate indicator of COVID-19 infection, by occupation type and age-group.

Results

Among company employees, statistical significance was identified in the 15- to 29-year and 30- to 59-year age-groups, showing higher fever rates in the non-teleworker group (for the 15- to 29-year age-group, non-teleworkers: 7.64%; teleworkers: 6.45%; P = 0.02; for the 30- to 59-year age-group, non-teleworkers: 3.46%; teleworkers: 3.14%; P = 0.02).

Conclusions

Telework remains a controversial topic in Japan as the government called for emergency measures. Although caution is warranted in interpreting our findings because our data are limited to the voluntary SNS users, they will be essential to push forward with more measures to promote social distancing measures in the midst of Japan's current tense political climate.

Antitumor activity of the PD-1/PD-L1 binding inhibitor BMS-202 in the humanized MHC-double knockout NOG mouse

Recently, the first series of small molecule inhibitors of PD-1/PD-L1 were reported by Bristol-Myers Squibb (BMS), which were developed using a homogeneous time-resolved fluorescence (HTRF)-based screening investigation of the PD-1/PD-L1 interaction. Additional crystallographic and biophysical studies showed that these compounds inhibited the interaction of PD-1/PD-L1 by inducing the dimerization of PD-L1, in which each dimer binds one molecule of the stabilizer at its interface. However, the immunological mechanism of the antitumor effect of these compounds remains to be elucidated. In the present study, we focused on BMS-202 (a representative of the BMS compounds) and investigated its antitumor activity using in vitro and in vivo experiments. BMS-202 inhibited the proliferation of strongly PD-L1-positive SCC-3 cells (IC₅₀ 15 μM) and anti-CD3 antibody-activated Jurkat cells (IC₅₀ 10 μM) in vitro. Additionally, BMS-202 had no regulatory effect on the PD-1 or PD-L1 expression level on the cell surface of these cells. In an in vivo study using humanized MHC-double knockout (dKO) NOG mice, BMS-202 showed a clear antitumor effect compared with the controls; however, a direct cytotoxic effect was revealed to be involved in the antitumor mechanism, as there was no lymphocyte accumulation in the tumor site. These results suggest that the antitumor effect of BMS-202 might be partly mediated by a direct off-target cytotoxic effect in addition to the immune response-based mechanism. Also, the humanized dKO NOG mouse model used in this study was shown to be a useful tool for the screening of small molecule inhibitors of PD-1/PD-L1 binding that can inhibit tumor growth via an immune-response-mediated mechanism.

Observation of the Radiative Decays of ϒ(1S) to χ_{c1}

We report the first observation of the radiative decay of the ϒ(1S) into a charmonium state. The significance of the observed signal of ϒ(1S)→γχ_{c1} is 6.3 standard deviations including systematics. The branching fraction is calculated to be B[ϒ(1S)→γχ_{c1}]=[4.7_{-1.8}^{+2.4}(stat)_{-0.5}^{+0.4}(sys)×10^{-5}]. We also searched for ϒ(1S) radiative decays into χ_{c0,2} and η_{c}(1S,2S), and set upper limits on their branching fractions. These results are obtained from a 24.9  fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider at a center-of-mass energy equal to the ϒ(2S) mass using ϒ(1S) tagging by the ϒ(2S)→ϒ(1S)π^{+}π^{-} transitions.

Outcome of maintenance systemic chemotherapy with drug-free interval for metastatic urothelial carcinoma

OBJECTIVE

Aiming to achieve long-term disease control, maintenance systemic chemotherapy (MSC) with a 1-3-month drug-free interval is continued in selected patients. We report our experience of MSC for metastatic urothelial carcinoma (UC).

METHODS

Of 228 metastatic UC patients treated with systemic chemotherapy, 40 (17.5%, 40/228) had continuously undergone MSC. Data on the regimen, cycle number, and reason for the discontinuation of MSC were also collected. We analyzed OS from the initiation of MSC until death or the last follow-up, using the log-rank test to assess the significance of differences.

RESULTS

The median number of cycles of chemotherapy was 6, and the responses were CR in 6, PR in 20, SD in 13, and PD in 1 before MSC. Gemcitabine plus CDDP or carboplatin was mainly performed as MSC (70%, 28/40). MSC was repeated quarterly in 30 (75%, 30/40), every two months in 8 (20%, 8/40), and with other intervals in 2 (5%, 2/40). Overall, a median of 3.5 cycles (range: 1-29) of MSC was performed. The reason for the discontinuation of MSC was PD in 24 (60%, 24/40), favorable disease control in 9 (22.5%, 9/40), and myelosuppression in 3 (7.5%, 3/40), and for other reasons in 2 (5%, 2/40). MSC was ongoing in 2 (5%, 2/40). The median OS was 27 months from the initiation of MSC. PS0 (P = 0.0169), the absence of lung metastasis (P = 0.0387), and resection of the primary site (P = 0.0495) were associated with long-term survival after MSC.

CONCLUSIONS

In selected patients, long-term systemic chemotherapy could be performed with a drug-free interval. Our maintenance strategy with cytotoxic drugs may become one of the treatment options for long-term disease control.

Risk model for severe postoperative complications after total pancreatectomy based on a nationwide clinical database

BACKGROUND

Total pancreatectomy is required to completely clear tumours that are locally advanced or located in the centre of the pancreas. However, reports describing clinical outcomes after total pancreatectomy are rare. The aim of this retrospective observational study was to assess clinical outcomes following total pancreatectomy using a nationwide registry and to create a risk model for severe postoperative complications.

METHODS

Patients who underwent total pancreatectomy from 2013 to 2017, and who were recorded in the Japan Society of Gastroenterological Surgery and Japanese Society of Hepato-Biliary-Pancreatic Surgery database, were included. Severe complications at 30 days were defined as those with a Clavien-Dindo grade III needing reoperation, or grade IV-V. Occurrence of severe complications was modelled using data from patients treated from 2013 to 2016, and the accuracy of the model tested among patients from 2017 using c-statistics and a calibration plot.

RESULTS

A total of 2167 patients undergoing total pancreatectomy were included. Postoperative 30-day and in-hospital mortality rates were 1·0 per cent (22 of 2167 patients) and 2·7 per cent (58 of 167) respectively, and severe complications developed in 6·0 per cent (131 of 2167). Factors showing a strong positive association with outcome in this risk model were the ASA performance status grade and combined arterial resection. In the test cohort, the c-statistic of the model was 0·70 (95 per cent c.i. 0·59 to 0·81).

CONCLUSION

The risk model may be used to predict severe complications after total pancreatectomy.

Impact of combination therapy with anti-PD-1 blockade and a STAT3 inhibitor on the tumor-infiltrating lymphocyte status

Recently, clinical studies using anti-immune checkpoint molecule antibodies have been successful in solid tumors, such as melanoma and non-small cell lung cancers. However, pancreatic cancers are still intractable and difficult to treat once recurrence or metastasis occurs; thus, novel combined use of immune checkpoint blockade (ICB) with molecular targeted drugs is considered a therapeutic option. Previously, we developed a novel humanized MHC-double knockout (dKO) NOG mouse model and demonstrated that an anti-PD-1 antibody or a STAT3 inhibitor showed anti-tumor effects through an immunological mechanism. In the current study, using a humanized mouse model, we aimed to develop a combination therapy with an anti-PD-1 antibody and a STAT3 inhibitor (STX-0119) for use in vivo against pancreatic cancer. In an in vitro investigation, STX-0119 showed weak to moderate cytotoxic activity against several pancreatic cancer cell lines, which exhibited activated pSTAT3 and weak PD-L1 expression. However, unexpectedly, an in vivo study indicated that the combination of the anti-PD-1 antibody with STX-0119 remarkably reduced the anti-tumor effect and TIL numbers despite the effective anti-tumor activity against pancreatic cancer was produced individually by STX-0119 and the anti-PD-1 antibody. These results suggested that the combination of an anti-PD-1 antibody with specific signal inhibiting drugs should be carefully evaluated to avoid unexpected side effects, and such studies might contribute to the development of an effective combination regimen of ICB with cancer-targeting drugs such as tyrosine kinase inhibitors (TKIs).

First Measurements of Absolute Branching Fractions of the Ξ_{c}^{0} Baryon at Belle

We present the first measurements of absolute branching fractions of Ξ_{c}^{0} decays into Ξ^{-}π^{+}, ΛK^{-}π^{+}, and pK^{-}K^{-}π^{+} final states. The measurements are made using a dataset comprising (772±11)×10^{6} BB[over ¯] pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB e^{+}e^{-} collider. We first measure the absolute branching fraction for B^{-}→Λ[over ¯]_{c}^{-}Ξ_{c}^{0} using a missing-mass technique; the result is B(B^{-}→Λ[over ¯]_{c}^{-}Ξ_{c}^{0})=(9.51±2.10±0.88)×10^{-4}. We subsequently measure the product branching fractions B(B^{-}→Λ[over ¯]_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}→Ξ^{-}π^{+}), B(B^{-}→Λ[over ¯]_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}→ΛK^{-}π^{+}), and B(B^{-}→Λ[over ¯]_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}→pK^{-}K^{-}π^{+}) with improved precision. Dividing these product branching fractions by the result for B^{-}→Λ[over ¯]_{c}^{-}Ξ_{c}^{0} yields the following branching fractions: B(Ξ_{c}^{0}→Ξ^{-}π^{+})=(1.80±0.50±0.14)%, B(Ξ_{c}^{0}→ΛK^{-}π^{+})=(1.17±0.37±0.09)%, and B(Ξ_{c}^{0}→pK^{-}K^{-}π^{+})=(0.58±0.23±0.05)%. For the above branching fractions, the first uncertainties are statistical and the second are systematic. Our result for B(Ξ_{c}^{0}→Ξ^{-}π^{+}) can be combined with Ξ_{c}^{0} branching fractions measured relative to Ξ_{c}^{0}→Ξ^{-}π^{+} to yield other absolute Ξ_{c}^{0} branching fractions.

Observation of Ξ(1620)^{0} and Evidence for Ξ(1690)^{0} in Ξ_{c}^{+}→Ξ^{-}π^{+}π^{+} Decays

We report the first observation of the double strange baryon Ξ(1620)^{0} in its decay to Ξ^{-}π^{+} via Ξ_{c}^{+}→Ξ^{-}π^{+}π^{+} decays based on a 980  fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The mass and width are measured to be 1610.4±6.0(stat)_{-4.2}^{+6.1} (syst)  MeV/c^{2} and 59.9±4.8(stat)_{-7.1}^{+2.8}(syst)  MeV, respectively. We obtain 4.0σ evidence of the Ξ(1690)^{0} with the same data sample. These results shed light on the structure of hyperon resonances with strangeness S=-2.

Observation of Transverse Λ/Λ[over ¯] Hyperon Polarization in e^{+}e^{-} Annihilation at Belle

We report the first observation of the spontaneous polarization of Λ and Λ[over ¯] hyperons transverse to the production plane in e^{+}e^{-} annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive Λ/Λ[over ¯] production, we also report results with subtracted feed-down contributions from Σ^{0} and charm. This measurement uses a dataset of 800.4  fb^{-1} collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV. We observe a significant polarization that rises with the fractional energy carried by the Λ/Λ[over ¯] hyperon.

Estimating the Net Utility Gains Among Donors and Recipients of Adult Living Donor Kidney Transplant

OBJECTIVES

Living donor kidney transplant relieves the disease burden of patients with end-stage renal disease but may shorten donor life expectancy; however, their quality of life (QOL) is preserved. Nevertheless, the magnitude of the net gain of this procedure is unknown. We evaluated the QOL of both donors and recipients concurrently and calculated the net utility gain.

METHODS

We recruited 210 subjects who visited the kidney transplantation clinic of a university hospital. Subjects were asked to complete the 5-level EQ-5D-based questionnaire, and patient characteristics were extracted from their medical records. We performed multivariate tobit models analysis to evaluate the QOL change caused by transplant surgery and subsequently ran computational simulations to determine the net utility gains of donors and recipients. We also performed sensitivity analyses.

RESULTS

After excluding 16 answers with missing data, we analyzed 203 answers in total. After the transplant surgery, recipients gained 0.07 in utility value while donors lost 0.04. In the net utility analysis, we found that the quality-adjusted life years gained ranged from 7.2 to 7.8 in the most favorable case observed in the combination of middle-aged recipients and elderly donors. Assuming no utility discount, the most favorable combination was that with older donors and younger recipients.

CONCLUSIONS

These findings indicated that the QOL improvement in recipients was larger than the loss among donors. When calculating the net utilities, a combination of middle-aged recipients and elderly donors yielded the largest net utility, but this was likely derived from assumption in the discount of QOL.

Search for a Light CP-odd Higgs Boson and Low-Mass Dark Matter at the Belle Experiment

We report on the first Belle search for a light CP-odd Higgs boson, A^{0}, that decays into low mass dark matter, χ, in final states with a single photon and missing energy. We search for events produced via the dipion transition ϒ(2S)→ϒ(1S)π^{+}π^{-}, followed by the on-shell process ϒ(1S)→γA^{0} with A^{0}→χχ, or by the off-shell process ϒ(1S)→γχχ. Utilizing a data sample of 157.3×10^{6} ϒ(2S) decays, we find no evidence for a signal. We set limits on the branching fractions of such processes in the mass ranges M_{A^{0}}<8.97  GeV/c^{2} and M_{χ}<4.44  GeV/c^{2}. We then use the limits on the off-shell process to set competitive limits on WIMP-nucleon scattering in the WIMP mass range below 5  GeV/c^{2}.

First Evidence for cos2β>0 and Resolution of the Cabibbo-Kobayashi-Maskawa Quark-Mixing Unitarity Triangle Ambiguity

We present first evidence that the cosine of the CP-violating weak phase 2β is positive, and hence exclude trigonometric multifold solutions of the Cabibbo-Kobayashi-Maskawa (CKM) Unitarity Triangle using a time-dependent Dalitz plot analysis of B^{0}→D^{(*)}h^{0} with D→K_{S}^{0}π^{+}π^{-} decays, where h^{0}∈{π^{0},η,ω} denotes a light unflavored and neutral hadron. The measurement is performed combining the final data sets of the BABAR and Belle experiments collected at the ϒ(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471±3)×10^{6}BB[over ¯] pairs recorded by the BABAR detector and (772±11)×10^{6}BB[over ¯] pairs recorded by the Belle detector. The results of the measurement are sin2β=0.80±0.14(stat)±0.06(syst)±0.03(model) and cos2β=0.91±0.22(stat)±0.09(syst)±0.07(model). The result for the direct measurement of the angle β of the CKM Unitarity Triangle is β=[22.5±4.4(stat)±1.2(syst)±0.6(model)]°. The measurement assumes no direct CP violation in B^{0}→D^{(*)}h^{0} decays. The quoted model uncertainties are due to the composition of the D^{0}→K_{S}^{0}π^{+}π^{-} decay amplitude model, which is newly established by performing a Dalitz plot amplitude analysis using a high-statistics e^{+}e^{-}→cc[over ¯] data sample. CP violation is observed in B^{0}→D^{(*)}h^{0} decays at the level of 5.1 standard deviations. The significance for cos2β>0 is 3.7 standard deviations. The trigonometric multifold solution π/2-β=(68.1±0.7)° is excluded at the level of 7.3 standard deviations. The measurement resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle.

Review: Challenges in the histopathological classification of ganglioglioma and DNT: microscopic agreement studies and a preliminary genotype-phenotype analysis

Low-grade epilepsy-associated brain tumours (LEAT) are the second most common cause for drug-resistant, focal epilepsy, that is ganglioglioma (GG) and dysembryoplastic neuroepithelial tumours (DNT). However, molecular pathogenesis, risk factors for malignant progression and their frequent association with drug-resistant focal seizures remain poorly understood. This contrasts recent progress in understanding the molecular-genetic basis and targeted treatment options in diffuse gliomas. The Neuropathology Task Force of the International League Against Epilepsy examined available literature to identify common obstacles in diagnosis and research of LEAT. Analysis of 10 published tumour series from epilepsy surgery pointed to poor inter-rater agreement for the histopathology diagnosis. The Task Force tested this hypothesis using a web-based microscopy agreement study. In a series of 30 LEAT, 25 raters from 18 countries agreed in only 40% of cases. Highest discordance in microscopic diagnosis occurred between GG and DNT variants, when oligodendroglial-like cell patterns prevail, or ganglion cells were difficult to discriminate from pre-existing neurons. Suggesting new terminology or major histopathological criteria did not satisfactorily increase the yield of histopathology agreement in four consecutive trials. To this end, the Task Force applied the WHO 2016 strategy of integrating phenotype analysis with molecular-genetic data obtained from panel sequencing and 450k methylation arrays. This strategy was helpful to distinguish DNT from GG variants in all cases. The Task Force recommends, therefore, to further develop diagnostic panels for the integration of phenotype-genotype analysis in order to reliably classify the spectrum of LEAT, carefully characterize clinically meaningful entities and make better use of published literature.

Observation of ϒ(2S)→γη_{b}(1S) Decay

We report the observation of ϒ(2S)→γη_{b}(1S) decay based on an analysis of the inclusive photon spectrum of 24.7  fb^{-1} of e^{+}e^{-} collisions at the ϒ(2S) center-of-mass energy collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We measure a branching fraction of B[ϒ(2S)→γη_{b}(1S)]=(6.1_{-0.7-0.6}^{+0.6+0.9})×10^{-4} and derive an η_{b}(1S) mass of 9394.8_{-3.1-2.7}^{+2.7+4.5}  MeV/c^{2}, where the uncertainties are statistical and systematic, respectively. The significance of our measurement is greater than 7 standard deviations, constituting the first observation of this decay mode.

Classification of tumor microenvironment immune types based on immune response-associated gene expression

In 2014, the Shizuoka Cancer Center launched project High‑tech Omics‑based Patient Evaluation (HOPE), which features whole exome sequencing (WES) and gene expression profiling (GEP) of fresh surgical specimens from cancer patients. With the development of clinical trials of programmed death‑1 (PD‑1)/PD‑ligand 1 (PD‑L1) blockade, PD‑L1 expression and a high tumor mutation burden become possible biomarkers that could be used to predict immune responses. In this study, based on WES and GEP data from 1,734 tumors from the HOPE project, we established a tumor microenvironment (TME) immune‑type classification consisting of 4 types to evaluate the immunological status of cancer patients and analyze immunological pathways specific for immune types. Project HOPE was conducted in accordance with the Ethical Guidelines for Human Genome and Genetic Analysis Research with the approval of the Institutional Review Board. Based on the expression level of the PD‑L1 and CD8B genes, the immunological status was divided into 4 types as follows: A, PD‑L1+CD8B+; B, PD‑L1+CD8B‑; C, PD‑L1‑CD8B‑; and D, PD‑L1‑CD8B+. Type A, with PD‑L1+ and CD8B+, exhibited an upregulation of cytotoxic T lymphocyte (CTL) killing‑associated genes, T‑cell activation genes, antigen‑presentation and dendritic cell (DC) maturation genes, and T‑cell‑attracting chemokine genes, which promoted Th1 antitumor responses. By contrast, type C, with PD‑L1‑ and CD8B‑, exhibited a low expression of T‑cell‑activating genes and an upregulation of cancer driver gene signaling, which suggested an immune‑suppressive status. With regard to hypermutator tumors, PD‑L1+ hypermutator cases exhibited a specific upregulation of the IL6 gene compared with the PD‑L1‑ cases. On the whole, our data indicate that the classification of the TME immune types may prove to be a useful tool for evaluating the immunological status and predicting antitumor responses and prognosis.

Observation of ϒ(4S)→η^{'}ϒ(1S)

We report the first observation of the hadronic transition ϒ(4S)→η^{'}ϒ(1S), using 496  fb^{-1} data collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We reconstruct the η^{'} meson through its decays to ρ^{0}γ and to π^{+}π^{-}η, with η→γγ. We measure B(ϒ(4S)→η^{'}ϒ(1S))=[3.43±0.88(stat)±0.21(syst)]×10^{-5}, with a significance of 5.7σ.

Observation of an Excited Ω^{-} Baryon

Using data recorded with the Belle detector, we observe a new excited hyperon, an Ω^{*-} candidate decaying into Ξ^{0}K^{-} and Ξ^{-}K_{S}^{0} with a mass of 2012.4±0.7(stat)±0.6(syst)  MeV/c^{2} and a width of Γ=6.4_{-2.0}^{+2.5}(stat)±1.6(syst)  MeV. The Ω^{*-} is seen primarily in ϒ(1S),ϒ(2S), and ϒ(3S) decays.

Search for B^{-}→μ^{-}ν[over ¯]_{μ} Decays at the Belle Experiment

We report the results of a search for the rare, purely leptonic decay B^{-}→μ^{-}ν[over ¯]_{μ} performed with a 711  fb^{-1} data sample that contains 772×10^{6}  BB[over ¯] pairs, collected near the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The signal events are selected based on the presence of a high momentum muon and the topology of the rest of the event showing properties of a generic B-meson decay, as well as the missing energy and momentum being consistent with the hypothesis of a neutrino from the signal decay. We find a 2.4 standard deviation excess above background including systematic uncertainties, which corresponds to a branching fraction of B(B^{-}→μ^{-}ν[over ¯]_{μ})=(6.46±2.22±1.60)×10^{-7} or a frequentist 90% confidence level interval on the B^{-}→μ^{-}ν[over ¯]_{μ} branching fraction of [2.9,10.7]×10^{-7}.

Abstract P2-11-11: Role of postmastectomy radiotherapy after neoadjuvant chemotherapy in breast cancer patients: A study from the Japanese breast cancer registry

Background:

Postmastectomy radiotherapy (PMRT) has been shown to be beneficial in node-positive breast cancer patients. However, the role of PMRT for patients receiving modern neoadjuvant chemotherapy (NAC) are controversial. We aimed to evaluate the efficacy of radiotherapy for breast cancer patients treated with NAC and mastectomy in the Japanese Breast Cancer Registry.

Methods:

Patients who received NAC and mastectomy for cT1-4 cN0-2 M0 breast cancer were included in this analysis. We assessed locoregional recurrence (LRR), distant disease-free survival (DDFS), and overall survival (OS) using the Kaplan-Meier method and compared them between the groups with and without PMRT by nodal status after NAC; ypN0, ypN1, and ypN2-3. We also performed multivariable cox regression analysis to evaluate the association of radiotherapy and these outcomes adjusting for baseline patient and cancer characteristics.

Results:

Of the 145,530 patients registered from 2004 to 2009, we identified 3,226 patients who met our inclusion criteria with the 5-year follow-up information including 1,299 ypN0, 1,036 ypN1, and 879 ypN2-3 cases. PMRT was performed in 185 patients (14.2%) with ypN0, 265 patients (25.6%) with ypN1, and 543 patients (61.8%) with ypN2-3. There was no difference in LRR, DDFS, and OS between the groups with and without radiotherapy for ypN1 patients who received NAC (P=0.72, P=0.29, and P=0.36, respectively). For patients with ypN2-3 breast cancer, radiotherapy significantly improved LRR (P&lt;0.001), DDFS (P=0.01), and OS (P&lt;0.001) on univariate analysis. No difference in LRR, DDFS, and OS was observed for ypN0 patients (P=0.81, P=0.15, and P=0.05, respectively). In multivariable analysis, the use of radiotherapy was independently associated with improved LRR [hazard ratio (HR): 0.608, 95% confidence interval (CI): 0.452–0.818, P=0.001] and OS [HR: 0.685, 95% CI: 0.531–0.885, P=0.004] for ypN2-3 patients.

Effect of PMRT on locoregional recurrence by the ypN subgroupsypN subgroupHazard ratio95%CI Low95%CI HighP valueypN00.8550.4581.5960.623ypN10.8320.5491.2620.387ypN2-30.6080.4520.8180.001

Immune response-associated gene profiling in Japanese melanoma patients using multi-omics analysis

Project High-tech Omics-based Patient Evaluation (HOPE), including comprehensive whole-exome sequencing (WES) and gene expression profiling (GEP) using freshly resected tumor specimens, has been in progress since its implementation in 2014. Among a total of 1,685 cancer patients, 13 melanoma patients were registered in the HOPE Project and were characterized using multi-omics analyses. Among the 13 melanoma patients, 4 were deceased, and 9 were alive. The mean overall survival (OS) and relapse‑free survival (RFS) times of the melanoma patients were 16.9 and 14.7 months, respectively. Previously, we developed an immune response‑associated gene list, which consisted of 164 genes in Project HOPE, for evaluating the immunological status. In the present study, the association of immune response‑associated gene expression with immunological parameters, such as programmed death-ligand 1 (PD-L1) and CD8 expression levels, single nucleotide variant (SNV) number, and Vogelstein driver gene mutation number, was investigated. With respect to PD-L1 expression, both immuno-suppression and immuno-stimulation-related genes were upregulated in PD-L1-positive melanomas. In contrast, regarding Vogelstein driver mutations, several T-cell activation-related genes were significantly downregulated in the high driver gene mutation group. In addition, many T-cell activation-related genes were upregulated in the CD8-positive melanomas. The correlation of immune response-associated gene expression with the survival time of the melanoma patients was investigated. Eight specific genes were commonly identified as genes that were significantly correlated for both the overall OS and RFS time, which could be possible prognostic factors for melanoma patients. These results revealed that an immune response-associated gene panel could be an informative tool for evaluating the immunological status prior to clinical immunotherapy in the upcoming era of genomic cancer medicine.

Evidence for Isospin Violation and Measurement of CP Asymmetries in B→K^{*}(892)γ

We report the first evidence for isospin violation in B→K^{*}γ and the first measurement of the difference of CP asymmetries between B^{+}→K^{*+}γ and B^{0}→K^{*0}γ. This analysis is based on the data sample containing 772×10^{6}BB[over ¯] pairs that was collected with the Belle detector at the KEKB energy-asymmetric e^{+}e^{-} collider. We find evidence for the isospin violation with a significance of 3.1σ, Δ_{0+}=[+6.2±1.5(stat)±0.6(syst)±1.2(f_{+-}/f_{00})]%, where the third uncertainty is due to the uncertainty on the fraction of B^{+}B^{-} to B^{0}B[over ¯]^{0} production in ϒ(4S) decays. The measured value is consistent with predictions of the standard model. The result for the difference of CP asymmetries is ΔA_{CP}=[+2.4±2.8(stat)±0.5(syst)]%, consistent with zero. The measured branching fractions and CP asymmetries for charged and neutral B meson decays are the most precise to date. We also calculate the ratio of branching fractions of B^{0}→K^{*0}γ to B_{s}^{0}→ϕγ.

Search for CP Violation and Measurement of the Branching Fraction in the Decay D^{0}→K_{S}^{0}K_{S}^{0}

We report a study of the decay D^{0}→K_{S}^{0}K_{S}^{0} using 921  fb^{-1} of data collected at or near the ϒ(4S) and ϒ(5S) resonances with the Belle detector at the KEKB asymmetric energy e^{+}e^{-} collider. The measured time-integrated CP asymmetry is A_{CP}(D^{0}→K_{S}^{0}K_{S}^{0})=(-0.02±1.53±0.02±0.17)%, and the branching fraction is B(D^{0}→K_{S}^{0}K_{S}^{0})=(1.321±0.023±0.036±0.044)×10^{-4}, where the first uncertainty is statistical, the second is systematic, and the third is due to the normalization mode (D^{0}→K_{S}^{0}π^{0}). These results are significantly more precise than previous measurements available for this mode. The A_{CP} measurement is consistent with the standard model expectation.