Identification of barriers to implementation of precision oncology in patients with rare cancers.

Established treatment options for rare cancers are limited by the small number of patients. The current comprehensive genomic profiling (CGP) testing might not fully exploit opportunities for precision oncology in patients with rare cancers. Therefore, we aimed to explore the factors associated with CGP testing utility in rare cancers and identify barriers to implementing precision oncology. Patients who underwent CGP testing at our institution between September 2019 and June 2021 were enrolled in this retrospective study. Based on their results, the patients received molecularly targeted drugs or immune checkpoint inhibitors. Univariate and multivariate analyses evaluated the association between patient characteristics and the proportion of patients receiving molecularly targeted drugs. Overall, 790 patients underwent CGP testing. Among them, 333 patients with rare cancers were identified, of whom 278 (83.5%) had actionable genomic alterations, 127 (38.1%) had druggable genomic alterations, and 25 (7.5%) received genomically matched therapy. The proportion of patients receiving molecularly targeted drugs was significantly higher among those with treatment options with evidence levels A-D (8.7%) than those without treatment options with evidence levels A-D (2.9%). A potential barrier to CGP testing utility in rare cancers is the limited number of molecularly targeted drugs with clinical evidence. We propose that CGP testing be performed in patients with rare cancers who have treatment options with evidence levels A-D to maximize CGP testing utility in real-world practice.

Association of D-dimer level with thrombotic events, bleeding, and mortality in Japanese patients with solid tumors: a Cancer-VTE Registry subanalysis.

BACKGROUND: The D-dimer test is a simple test frequently used in routine clinical screening for venous thromboembolism (VTE). The Cancer-VTE Registry was a large-scale, multicenter, prospective, observational study in Japanese patients with cancer. This study aimed to clarify the relationship between D-dimer level at cancer diagnosis (baseline) and the incidence of events during cancer treatment (1-year follow-up period). METHODS: This was a post hoc sub-analysis of patients from the Cancer-VTE Registry whose D-dimer levels were measured at baseline. The incidence of events during the 1-year follow-up period was evaluated stratified by baseline D-dimer level. Adjusted hazard ratios for D-dimer level and events during the follow-up period were evaluated. RESULTS: Among the total enrolled patients, baseline D-dimer level was measured in 9020 patients. The mean ± standard deviation baseline D-dimer level was 1.57 ± 3.94 µg/mL. During the follow-up period, the incidence of VTE, cerebral infarction/transient ischemic attack (TIA)/systemic embolic events (SEE), bleeding, and all-cause death increased with increasing baseline D-dimer level. The incidence of all-cause death increased with increasing D-dimer level regardless of cancer stage. The adjusted hazard ratio of all-cause death was 1.03 (95% confidence interval: 1.02-1.03) per 1.0-µg/mL increase in baseline D-dimer level. CONCLUSIONS: Increases in D-dimer levels were associated with a higher risk of thrombotic events, such as VTE and cerebral infarction/TIA/SEE, during cancer treatment. Furthermore, higher D-dimer levels at cancer diagnosis were associated with a higher mortality rate, regardless of cancer stage.

Incidence and factors associated with stent dysfunction and pancreatitis after gastroduodenal stenting for malignant gastric outlet obstruction.

Background and study aims Endoscopic gastroduodenal stent (GDS) deployment is currently a standard treatment for malignant gastric outlet obstruction (mGOO) in patients with limited life expectancy; however, stent dysfunction (SD) and complicated pancreatitis often occur after GDS deployment. We investigated incidence and contributing factors of SD and complicated pancreatitis. Patients and methods We retrospectively reviewed 203 patients who underwent initial GDS deployment for palliation of mGOO symptoms between October 2017 and July 2022, including 109 who underwent GDS deployment across the duodenal papilla (sub-cohort). Results SDs, including tumor ingrowth (n = 26), kinking (n = 14), and migration (n = 13), occurred in 68 patients (33.5%). Cumulative SD incidence was 41.1% (95% confidence interval, 32.6-49.4%). SD incidence increased to 0.4%, 0.16%, and 0.06% per day at < 8, 8-16, and>16 weeks, respectively. On multivariate analysis, Niti-S pyloric/duodenal stent deployment (sub-distribution hazard ratio [sHR] 0.26, P = 0.01) and survival length ≥ 90 days (sHR 2.5, P = 0.01) were respectively identified as favorable and risk factors significantly associated with SD. Pancreatitis developed in 14 patients (12.8%) in the sub-cohort, which had significantly higher parenchymal diameter ( P < 0.01) and lower main pancreatic duct (MPD) caliber ( P < 0.01) than the non-pancreatitis cohort. On multivariate analysis, MPD caliber < 3 mm independently predicted pancreatitis (odds ratio 6.8, P = 0.03). Conclusions Deployment of the Niti-S pyloric/duodenal stent, with conformability even for angulated strictures, significantly reduced the incidence of SD. Stent selection, life expectancy, and MPD caliber should be taken into consideration during decision-making for GDS deployment for mGOO.

Safety of biliary drainage with 6-mm metallic stent for preoperative obstructive jaundice in pancreatic cancer: PURPLE SIX STUDY.

BACKGROUND AND AIM: The 10-mm self-expandable metal stent (SEMS) is the standard for endoscopic transpapillary biliary drainage before pancreatic cancer surgery. However, the efficacy of stents thinner than 10 mm has not been adequately validated. Therefore, we aimed to evaluate the safety of a 6-mm fully covered SEMS (FCSEMS) for distal malignant biliary obstruction (DMBO) during preoperative chemotherapy for pancreatic cancer. METHODS: This was a single-arm, multicenter, prospective phase II study of endoscopic transpapillary initial biliary drainage for DMBO before pancreatic cancer surgery. The primary endpoint was stent-related adverse events, and the key secondary endpoint was the non-recurrent biliary obstruction (non-RBO) rate during the observation period for both resectable (R) and borderline resectable (BR) pancreatic cancers. RESULTS: The study enrolled 33 patients, among whom 32 received the study treatment. There were 23 and 9 cases of R and BR pancreatic cancers, respectively. The technical and clinical success rates were 97.0% and 90.1%, respectively. The stent-related adverse event rate was 3.1% (n = 1, acute pancreatitis) (95% confidential interval, 0.00-16.2), which met the criteria to be considered safe. The overall non-RBO rate during the observation period (median 96 days) was 78.1% (82.6% and 66.7% for R and BR pancreatic cancer cases, respectively). CONCLUSIONS: The 6-mm FCSEMS is an extremely safe metallic stent with a low stent-related adverse event rate of 3.1% for preoperative biliary drainage in pancreatic cancer. It is considered the optimal stent for preoperative biliary drainage in terms of the non-RBO rate. UMIN Clinical Trial Registry (UMIN-CTR 000041704).

Viscosity and Characteristics of Malignant Ascites.

BACKGROUND/AIM: Malignant ascites is a common condition in patients with terminal cancer. Treatments, such as diuretics, percutaneous drainage of ascites, and abdominal vein shunting have been advocated. However, these treatments have not achieved sufficient palliative effects. Therefore, the development of innovative therapies is mandated, especially for new therapies that require the creation of a fluid simulation of malignant ascites. However, there have been no previous studies on the physical properties of malignant ascites, including viscosity, which are necessary for the development of such a fluid. Therefore, we prospectively investigated the physical properties of malignant ascites. PATIENTS AND METHODS: This single-center, prospective, observational study included 30 patients between November 2021 and January 2023. The primary endpoint was the viscosity of the malignant ascites, and the secondary endpoints included other viscosity studies, biochemical tests, and the presence of malignant cells in the ascites. RESULTS: The median viscosity was 1.105 mPa*S. The viscosity of malignant ascites tended to decrease with increasing temperature, which is common for liquids. Malignant ascites fluid containing malignant cells tended to be more viscous than ascites fluid without malignant cells; furthermore, albumin levels tended to be higher in the former than in the latter. CONCLUSION: Malignant ascites' median viscosity was 1.105 mPa*S. Correlation between viscosity and temperature showed a decreasing trend. These findings contribute valuable insights for future malignant ascites management and device development.

Early Tumor Shrinkage and Depth of Response as Predictors of Survival for Advanced Biliary Tract Cancer: An Exploratory Analysis of JCOG1113.

BACKGROUND: Recent studies suggest that early tumor shrinkage (ETS) and depth of response (DpR) reflect outcomes of chemotherapy in various cancers. This study evaluated the association of ETS and DpR with clinical outcomes using data from JCOG1113, which demonstrated the non-inferiority of gemcitabine plus S-1 (GS) to gemcitabine plus cisplatin (GC) for chemotherapy-naïve advanced biliary tract cancer. MATERIAL AND METHODS: In total, 354 (289 with measurable target lesions) patients enrolled in JCOG1113 were divided into ETS-unachieved and ETS-achieved groups (≥20% tumor reduction at week 6) and DpR-low and DpR-high groups (≥40% maximum shrinkage) until 12 weeks after enrollment. The impact of ETS and DpR on survival outcome was evaluated using the multivariable Cox proportional hazard model. RESULTS: The proportions of patients in the ETS-achieved and DpR-high groups were similar between the 2 treatment arms. The hazard ratios (HRs) of progression-free survival (PFS) and overall survival (OS) for the ETS-achieved group were 0.70 (95% confidence interval (CI), 0.52-0.93) and 0.60 (95%CI, 0.44-0.81), respectively. The HRs of PFS and OS for the DpR-high group were 0.67 (95%CI, 0.48-0.94) and 0.64 (95%CI, 0.46-0.90), respectively. In the subpopulation treatment effect pattern plot analysis, most patients in the ETS-achieved group in the GC arm did not experience disease progression after 12 weeks from the landmark. CONCLUSION: As on-treatment markers, ETS and DpR were effective tools. ETS was clinically useful, because it can be used to evaluate the outcomes of treatment early at a specific time.

Feasibility of S-1 adjuvant chemotherapy after major hepatectomy for biliary tract cancers: An exploratory subset analysis of JCOG1202.

INTRODUCTION: Major hepatectomy (MH) may produce the impaired liver function and affect the feasibility of adjuvant chemotherapy in terms of early period after the surgery, but there have not been detailed investigations. JCOG1202 (UMIN000011688) is a randomized phase III trial demonstrating the superiority of adjuvant S-1 chemotherapy for biliary tract cancer (BTC). The aim of this study is to examine the influence of MH for BTC on adjuvant S-1. MATERIALS AND METHODS: Of the total 424 patients, 207 received S-1 (S-1 arm) while the remaining 217 were not. We compared MH with non-major hepatectomy (NMH) for BTC. RESULTS: In the S-1 arm, 42 had undergone MH, and 165 had undergone NMH. MH had similar pretreatment features to NMH, including the proportion of biliary reconstruction, to NMH, except for a lower platelet count (17.7 vs. 23.4 × 104/mm3, p < 0.0001) and lower serum albumin level (3.5 vs. 3.8 g/dL, p < 0.0001). The treatment completion proportion tended to be lower for MH than for NMH (59.5 % vs. 75.8 %; risk ratio, 0.786 [95 % confidence interval, 0.603-1.023], p = 0.0733), and the median dose intensity was lower as well (88.7 % vs. 99.6 %, p = 0.0358). The major reasons for discontinuation were biliary tract infections and gastrointestinal disorders after MH. The frequency of grade 3-4 biliary tract infection was 19.0 % in MH vs. 4.2 % in NMH. CONCLUSION: The treatment completion proportion and dose intensity were lower in MH than in NMH. Caution should be exercised against biliary tract infections and gastrointestinal disorders during adjuvant S-1 after MH for BTC.

Development of a nomogram to predict survival in advanced biliary tract cancer.

The prognosis of advanced biliary tract cancer (BTC) patients remains poor due to limited efficacy of chemotherapy and difficulties in management. Thus, prediction of survival is crucial for the clinical management of advanced BTC. The aim was to develop and validate a nomogram to predict 6-month and 12-month survival in advanced BTC patients treated with chemotherapy. A multivariable Cox regression model was used to construct a nomogram in a training set (JCOG1113, a phase III trial comparing gemcitabine plus S-1 [GS] and gemcitabine plus cisplatin, n = 351). External validity of the nomogram was assessed using a test set (JCOG0805, a randomized, phase II trial comparing GS and S-1 alone, n = 100). Predictive performance was assessed in terms of discrimination and calibration. The constructed nomogram included lymph node metastasis, liver metastasis, carbohydrate antigen 19-9, carcinoembryonic antigen, albumin, and C-reactive protein. Uno's concordance index was 0.661 (95% confidence interval [CI] 0.629-0.696) in the training set and 0.640 (95% CI 0.566-0.715) in the test set. The calibration plots for 6-month and 12-month survival showed good agreement in the two analysis sets. The present nomogram can facilitate prediction of the prognosis of advanced BTC patients treated with chemotherapy and help clinicians' prognosis-based decision-making.

Study protocol for a prospective, multicentre, phase II trial on endoscopic treatment using two fully covered self-expandable metallic stents for benign strictures after hepaticojejunostomy.

INTRODUCTION: The current endoscopic treatment for postoperative benign hepaticojejunostomy anastomotic stricture (HJAS) has a high technical success rate and is highly effective in the short term. However, long-term results have shown a high rate of stenosis recurrence, which indicates an insufficient response to treatment. Three prospective studies on fully covered self-expandable metallic stent (FC-SEMS) treatment for benign HJAS used the stenosis resolution rate as the primary endpoint, and no study has yet used the long-term non-stenosis rate (at 12 months) as the primary endpoint. METHODS AND ANALYSIS: We launched the 'saddle-cross study', which will be conducted as a multicentre, prospective intervention of endoscopic treatment using two modified FC-SEMSs (BONASTENT️ M-Intraductal) that have been improved for benign stenosis in patients with benign HJAS, with the long-term non-restenosis rate (at 12 months) as the primary endpoint. This study aims to evaluate the long-term non-restenosis rate (at 12 months) and safety of the saddle-cross technique for benign HJAS. We plan to enrol 50 participants. ETHICS AND DISSEMINATION: This study has been approved by the Certified Review Board of the National Cancer Center, Japan (CRB3180009). The results will be reported at various conferences and published in international peer-reviewed journals.

Clinical features of germline BRCA1/2 or ATM pathogenic variant positive pancreatic cancer in Japan.

BACKGROUND: There has been increasing interest into the role of germline BRCA1/2 pathogenic variants (gBRCA PV) and gATM PV and likely PV (PV and LPV; PV + LPV) in the carcinogenesis and treatment of pancreatic cancer (PC), but the clinical features have not been well described. METHODS: Patients with confirmed gBRCA PV and gATM PV + LPV PC treated at our hospital between April 2016 and December 2021, were retrospectively evaluated for clinical characteristics and outcomes. RESULTS: Twenty-two patients harbored gBRCA PV and three patients harbored gATM PV + LPV. Of the gBRCA PV patients, 81.8 % received platinum-based chemotherapy with favorable treatment outcomes with an objective response rate of 50.0 % (95 % CI: 23.0-77.0), median progression free survival (PFS) of 334 days, and median overall survival (OS) of 926 days from the initiation of first-line chemotherapy. The annual number of patients with gBRCA PV was two patients per year before January 2021 (when BRACAnalysis became available in Japan), and ten patients during the 10 months thereafter. Four patients (20 %) with gBRCA PV developed soft-tissue metastasis with progression. Two patients with gATM PV + LPV received platinum-based chemotherapy and the best response of those patients was partial response and stable disease and their OS from the initiation of first-line chemotherapy was 1192 and 989 days, and PFS was 579 and 140 days, respectively. CONCLUSION: The diagnosis of gBRCA PV-positive PC has increased revealed in recent years. These tumors appear to be sensitive to platinum-based chemotherapy, with long term survival observed in gATM PV + LPV-positive patients.

Prospective clinical trial of EUS-guided choledochoduodenostomy without fistula dilation for malignant distal biliary obstruction.

Background and Objectives: During EUS-guided choledochoduodenostomy (EUS-CDS), fistula dilation before stent insertion is associated with adverse events (AEs), such as bile leakage and peritonitis. We hypothesized that EUS-CDS without fistula dilation using a novel self-expandable metal stent (SEMS) with a thin delivery system could overcome this problem, and we conducted this study to evaluate its feasibility and safety. Methods: This was an open-label, single-arm, phase II study at a single institution. We planned EUS-CDS without fistula dilation using a fully covered SEMS with a 5.9-Fr delivery system for unresectable malignant distal biliary obstruction. The primary outcome was overall technical success. Secondary outcomes were technical success without fistula dilation, procedure time, functional success, time to recurrent biliary obstruction, and AEs. The planned sample size was 25 patients. Results: In total, 24 patients were included in this study. In 21 patients, EUS-CDS was performed as primary drainage. The overall technical success rate was 100% (24 of 24 patients). The technical success rate without fistula dilation was 96% (23 of 24). The median procedure time was 16 min (range, 10-66 min). The functional success rate was 96% (23 of 24). The median time to recurrent biliary obstruction was 148 days (95% confidence interval, 29-266 days). There were no procedure-related AEs. Furthermore, computed tomography immediately after the procedure showed no leakage of contrast medium into the abdominal cavity in any patient. Conclusions: EUS-guided choledochoduodenostomy without fistula dilation using a fully covered SEMS with a 5.9-Fr delivery system is feasible with a high probability and can be achieved quickly while effectively preventing bile leakage and peritonitis.

Two Cases of Disseminated Alveolar Echinococcosis: The Diagnosis, Management, and Differential Considerations for Liver Lesions.

Alveolar echinococcosis (AE), caused by Echinococcus multilocularis, is an aggressive and potentially critical infestation that primarily affects the liver and can metastasize to any part of the body. We herein report two cases of echinococcosis, which could be differentiated from malignancy on imaging studies, with infections of the liver and mediastinal lymph nodes, and also associated with systemic disseminated lesions. AE is a very invasive infectious disease, and in order to detect such lesions at an early stage when they are still resectable, it is necessary to understand the characteristic imaging findings and determine the patient's current medical history.

Plain language summary of the TOPAZ-1 study: durvalumab and chemotherapy for advanced biliary tract cancer.

WHAT IS THIS SUMMARY ABOUT?: This is a summary describing the results of a Phase III study called TOPAZ-1. The study looked at treatment with durvalumab (a type of immunotherapy) and chemotherapy to treat participants with advanced biliary tract cancer (BTC). Advanced BTC is usually diagnosed at late stages of disease, when it cannot be cured by surgery. This study included participants with advanced BTC who had not received previous treatment, or had their cancer come back at least 6 months after receiving treatment or surgery that aimed to cure their disease. Participants received treatment with durvalumab and chemotherapy or placebo and chemotherapy. The aim of this study was to find out if treatment with durvalumab and chemotherapy could increase the length of time that participants with advanced BTC lived, compared with placebo and chemotherapy. WHAT WERE THE RESULTS OF THE STUDY?: Participants who took durvalumab and chemotherapy had a 20% lower chance of experiencing death at any point in the study compared with participants who received placebo and chemotherapy. The side effects experienced by participants were similar across treatment groups, and less than 12% of participants in either treatment group had to stop treatment due to treatment-related side effects. WHAT DO THE RESULTS OF THE STUDY MEAN?: Overall, these results support durvalumab and chemotherapy as a new treatment option for people with advanced BTCs. Based on the results of this study, durvalumab is now approved for the treatment of adults with advanced BTCs in combination with chemotherapy by government organizations in Europe, the United States and several other countries.

Incidence and risk factors for venous thromboembolism in the Cancer-VTE Registry pancreatic cancer subcohort.

BACKGROUND: This substudy of the Cancer-VTE Registry estimated venous thromboembolism (VTE) incidence and risk factors in pancreatic cancer patients. METHODS: The Cancer-VTE Registry was an observational study that collected VTE data from patients with solid tumors across Japan. We measured baseline VTE prevalence, and at 1-year follow-up, the cumulative incidence of symptomatic and composite VTE (symptomatic VTE and incidental VTE requiring treatment), bleeding, cerebral infarction/transient ischemic attack (TIA)/systemic embolic event (SEE), and all-cause death. RESULTS: Of 1006 pancreatic cancer patients, 86 (8.5%) had VTE at baseline, and seven (0.7%) had symptomatic VTE. Significant risk factors of baseline VTE were Eastern Cooperative Oncology Group performance status (ECOG PS) of 1, body mass index (BMI) ≥ 25 kg/m2, history of VTE, D-dimer > 1.2 µg/mL, and hemoglobin < 10 g/dL. At 1-year follow-up, the cumulative incidence of events was higher for pancreatic cancer vs other cancers. Pancreatic cancer patients with VTE vs those without VTE had significantly higher incidences of bleeding, cerebral infarction/TIA/SEE, and all-cause death. No significant risk factors for composite VTE were identified. CONCLUSIONS: The cumulative incidence of composite VTE during cancer treatment was higher in pancreatic cancer than in other cancer types. Some risk factors for VTE prevalence at cancer diagnosis were identified. Although VTE prevalence at cancer diagnosis did not predict the subsequent 1-year incidence of composite VTE, it was a significant predictor of other events such as all-cause death in pancreatic cancer patients. TRIAL REGISTRATION: UMIN Clinical Trials Registry; UMIN000024942.

Clinicopathological Findings and Treatment Outcomes of Patients with Primary Hepatobiliary Neuroendocrine Neoplasms: A Retrospective Single-institution Analysis.

Objective Primary hepatobiliary neuroendocrine neoplasms (NENs) are rare tumors exhibiting several morphological and behavioral characteristics. Considering the lack of relevant data on this topic, we evaluated the clinicopathological features and treatment outcomes of patients with primary hepatobiliary NENs. Methods/Patients We examined 43 consecutive patients treated at the National Cancer Center Hospital with pathological diagnoses of primary hepatobiliary NEN between 1980 and 2016. Results Nine patients were diagnosed with neuroendocrine tumor (NET) G1, 9 with NET G2, and 25 with neuroendocrine carcinoma (NEC) based on the World Health Organization 2019 classification. Patients with NEC had primary sites across the hepatobiliary organs, although sites in patients with NET G1 and NET G2 only included the liver and ampulla of Vater. Patients with primary extrahepatic bile duct or ampulla of Vater NENs tended to be diagnosed earlier than patients with primary gallbladder NENs. The median survival times in the NET G1, NET G2, and NEC groups were 167.9, 97.4, and 11.1 months, respectively. A good performance status, absence of distant metastases, and low tumor grade were identified as independent predictors of a favorable prognosis. Conclusion The NET-to-NEC ratio and tumor stage distribution at the diagnosis differed depending on the primary site. Patients with G1 and G2 NETs who underwent surgical resection had good prognoses, whereas those with NEC exhibited more advanced disease and poorer prognoses. The performance status, staging classification, and tumor grade are important factors to consider when devising an appropriate treatment strategy and predicting the prognoses of patients with primary hepatobiliary NEN.

A Multicenter Survey on Eligibility for a Randomized Phase III Trial of Adjuvant Chemotherapy for Resected Biliary Tract Cancer (JCOG1202, ASCOT).

BACKGROUND: The Adjuvant S-1 for Cholangiocarcinoma Trial (JCOG1202, [ASCOT]) was a multicenter, randomized controlled trial aimed at investigating the efficacy and safety of adjuvant chemotherapy (AC) with S-1 for resected biliary tract cancer (BTC). This trial reported that overall survival was prolonged with AC compared with observation. METHODS: With the aim of increasing enrollment, the present survey biannually recorded the number of patients eligible for enrollment into ASCOT and reasons for ineligibility among patients who had undergone surgery for BTC from April 2015 to September 2017 at 36 institutions participating in ASCOT. RESULTS: Of 2039 patients who underwent surgery for BTC, 211 (10.3%) were already enrolled, 166 (8.1%) were eligible but had not been enrolled, and 1662 (81.5%) were ineligible. Among ineligible patients, the predominant reasons for ineligibility were patient refusal (n = 332, 20.0%), pathologic stage (pT1N0; n = 248, 14.9%), age (≥ 81 years; n = 196, 11.8%), and prolonged postoperative complications (n = 176, 10.6%). CONCLUSIONS: Patients undergoing surgery for BTC are a heterogeneous cohort comprising patients with earlier pathologic stage, advanced age, and prolonged postoperative complications. These factors should be considered during the design of future clinical trials of perioperative treatments for resectable BTC.

Efficacy of endoscopic ultrasound-guided tissue acquisition for solid pancreatic lesions 20 mm or less in diameter suspected as neuroendocrine tumors or requiring differentiation.

BACKGROUND: For non-functioning pancreatic neuroendocrine tumors (pNETs) ≤ 20 mm, most guidelines consider follow-up observations as an option; however, the various treatment strategies are defined by size alone, even though the Ki-67 index is important for malignancy grading. Endoscopic ultrasound-guided tissue acquisition (EUS-TA) is the standard for the histopathological diagnosis of solid pancreatic lesions; however, recent results for small lesions remain unclear. Therefore, we examined the efficacy of EUS-TA for solid pancreatic lesions ≤ 20 mm suspected as pNETs or requiring differentiation and the non-increase rate in tumor size in follow-up cases. METHODS: We retrospectively analyzed data of 111 patients (median age = 58 years) with lesions ≤ 20 mm suspected as pNETs or requiring differentiation who underwent EUS-TA. All patients underwent specimen evaluation by rapid onsite evaluation (ROSE). RESULTS: EUS-TA led to a diagnosis of pNETs in 77 patients (69.4%) and tumors other than pNETs in 22 patients (19.8%). The histopathological diagnostic accuracy of EUS-TA was 89.2% (99/111) overall, 94.3% (50/53) for 10-20 mm lesions, and 84.5% (49/58) for ≤ 10 mm lesions, with no significant difference in diagnostic accuracy (p = 0.13). The Ki-67 index was measurable in all patients with a histopathological diagnosis of pNETs. Among 49 patients with a diagnosis of pNETs who were followed up, one patient (2.0%) showed tumor enlargement. CONCLUSIONS: EUS-TA for solid pancreatic lesions ≤ 20 mm suspected as pNETs or requiring differentiation is safe and has adequate histopathological diagnostic accuracy, suggesting that follow-up observations of pNETs with a histological pathologic diagnosis are acceptable in the short term.