Background: Information on rare hepatobiliary and pancreatic (HBP) subtypes of cancer is scarce. We aimed to elucidate the incidence and clinical features of rare tumors in Japan using the National Cancer Registry (NCR), a new nationwide integrated population-based registry. Methods: The data of patients diagnosed in 2016–2017 were extracted from the NCR database, and classified by topography: liver cells, intrahepatic bile duct, gallbladder, extrahepatic bile duct, ampulla of Vater, and pancreas. Data were described and analyzed using the World Health Organization and General Rules tumor classifications. The incidences for all rare tumors including hepatoblastoma and adenosquamous cell carcinoma were calculated as the number of new cases divided by the corresponding total person years. Results: The NCR data yielded 8,239 patients with rare HBP tumors between 2016 and 2017. The ratios of rare tumors to all cancer types were 0.5%, 0.7%, 3.9%, 1.6%, 0.8%, and 7.2% in the liver, intrahepatic bile duct, gallbladder, extrahepatic bile duct, ampulla of Vater, and pancreas, respectively. Rare tumors occurred more frequently in men, except for gallbladder tumors. The main tumor stage was localized in liver cells (42.4%) and the intrahepatic bile duct (51.6%); more patients were diagnosed in advanced stage with gallbladder (84.1%) and extrahepatic bile duct (74.4%) tumors. Approximately equal percentage of patients were diagnosed at designated cancer care hospitals (DCCHs) and non-DCCHs, whereas 60% to 70% patients received treatment at DCCHs. Conclusion: This is the first report to provide comprehensive information on the epidemiological status of rare HBP tumors in Japan by utilizing population-based NCR data.

Combined hepatocellular cholangiocarcinoma (cHCC-CCA) is a rare subtype of primary liver cancers. Therapeutic strategies for patients with cHCC-CCA are limited, and no standard systemic treatment has been established for unresectable cHCC-CCA. Here, we present six cases of cHCC-CCA treated with atezolizumab plus bevacizumab. We observed three partial responses and one stable disease as the best responses; two of these patients were still being treated with atezolizumab plus bevacizumab at the time of reporting (at least five months of treatment), whereas the remaining two patients were unable to continue treatment owing to adverse events. Atezolizumab plus bevacizumab may be an effective treatment for unresectable cHCC-CCA.

Background and objective: Endoscopic retrograde cholangiopancreatography (ERCP) is the gold standard for managing malignant biliary obstruction (MBO), but it is challenging in patients with surgically altered anatomy (SAA). EUS-guided hepaticogastrostomy (EUS-HGS) and enteroscopy-assisted ERCP are alternative techniques, but their comparative efficacy and safety in this population are not well-researched. Herein, we evaluated the outcomes of EUS-HGS versus single-balloon–assisted enteroscopy ERCP (SBE-ERCP) in MBO patients with SAA. Patients and methods: This retrospective study included 70 patients with MBO who underwent EUS-HGS (n = 29) or SBE-ERCP (n = 41) at a single center between April 2015 and June 2024. Data on the patient characteristics, procedure details, time to recurrent biliary obstruction (TRBO), and adverse events (AEs) were analyzed. Results: The EUS-HGS group showed a higher technical success rate (100% vs. 68%, P = 0.002), shorter procedure time (23 vs. 50 min, P < 0.001), and longer TRBO (251 vs. 103 d, P = 0.020) as compared with the SBE-ERCP group. Subgroup analysis revealed that pancreatobiliary cancer and SBE-ERCP were significantly associated with a shorter TRBO. When stratified by stent type, the median TRBO in the SBE-ERCP with PS group was 49 days, serving as the reference. In comparison, the median TRBO was 140 days in the SBE-ERCP with the self-expandable metallic stent group (hazard ratio [HR], 0.46; P = 0.181), 127 days in the EUS-HGS with PS group (HR, 0.38; P = 0.055), and 701 days in the EUS-HGS with the self-expandable metallic stent group (HR, 0.13; P = 0.014). The overall incidence of AEs was comparable between the 2 groups (20.6% vs. 17.1%), and there were no severe AEs. Regarding reintervention, there was no significant difference in technical success rate and procedure time between EUS-HGS and SBE-ERCP. Conclusion: EUS-HGS was associated with a superior technical success rate, shorter procedure time, and longer stent patency, without an increased risk of AEs, as compared with SBE-ERCP. Thus, EUS-HGS should be appropriate for managing MBO patients with SAA.

Cancer genome profiling (CGP) occasionally identifies pathogenic germline variants (PGV) in cancer susceptibility genes (CSG) as secondary findings. Here, we analyzed the prevalence and clinical characteristics of PGVs based on nationwide real-world data from CGP tests in Japan. We analyzed the genomic information and clinical characteristics of 23,928 patients with solid cancers who underwent either tumor-only (n = 20,189) or paired tumor-normal (n = 3,739) sequencing CGP tests between June 2019 and December 2021 using the comprehensive national database. We assigned clinical significance for all variants and highlighted the prevalence and characteristics of PGVs. Our primary analysis of the tumor-normal sequencing cohort revealed that 152 patients (4.1%) harbored PGVs in 15 CSGs. Among 783 germline variants, 113 were annotated as PGVs, 70 as benign variants, and 600 as variants of uncertain significance. The number of PGVs identified was highest in BRCA1/2, with 56, followed by TP53, with 18. PGVs were the most prevalent in ovarian and peritoneal cancers, including among cancer types common in Asia. In the tumor-only sequencing cohort, of the 5,184 pathogenic somatic variants across 26 CSGs, 784 (15.1%) were extracted according to the European Society for Medical Oncology recommendations for germline-focused tumor analysis. The prevalence of PGVs was similar to that previously reported in Europe and the United States. This is the largest analysis based on real-world tumor-normal sequencing tests in Asia. The more widespread use of the tumor-normal sequencing CGP test could be reasonable for evaluating PGVs. Significance: We analyzed real-world data from over 23,000 patients in Japan, revealing 4.1% harbored PGVs, particularly in BRCA1/2 and TP53, in CSGs. It highlights the prevalence of PGVs in Asian populations and supports the broader adoption of tumor-normal sequencing CGP tests for PGV evaluation.

Background: Although activation of human epidermal growth factor receptor 3 (HER3) is linked to resistance to targeted therapies in several cancer types, the HER3 expression profile during pancreatic cancer treatment remains unknown.Aims: We evaluated the HER3 expression status after chemotherapy for pancreatic cancer and its association with clinicopathological features and clinical outcomes.Materials & Methods: We included patients with pancreatic cancer who underwent chemotherapy and whose post‐treatment archival tissue specimens were collected. HER3 expression was retrospectively assessed by immunohistochemistry scoring (0, 1+, 2+, and 3+) of the membranous staining intensity.Results: HER3 expression after chemotherapy was evaluated in 41 patients, with matched‐pair analysis in five patients before and after chemotherapy. HER3 expression was observed in most of the patients after chemotherapy, demonstrating IHC scores of ≥ 1+ and ≥ 2+ in 40 (98%) and 26 (63%) of 41 patients, respectively. Of the 38 patients with adenocarcinoma, the median overall survival in the HER3 (2+/3+) and HER3 (0/1+) groups was 21.0 and 17.1 months, respectively. The comparison of HER3 expression before and after chemotherapy performed in five cases revealed that scores changed from 2+/3+ to 0/1+ in one case, 0/1+ to 2+/3+ in another case, and remained at 2+/3+ in three cases. Cancer genome profiling tests in eight cases found no HER3 amplification or mutation, and seven of these cases had adenocarcinomas with KRAS and TP53 mutations.Conclusion: A high prevalence of HER3 expression was observed in pancreatic cancer patients after chemotherapy. Our findings indicate that HER3 is a potential therapeutic target for pancreatic cancer, deserving further clinical investigation.

Aim: We conducted this observational study to investigate patterns of fibroblast growth factor receptor 2 ( FGFR2 ) fusions or rearrangements, and how they relate to other characteristics of patients with unresectable advanced cholangiocarcinoma. Methods: Patients aged 20 years or older with intrahepatic cholangiocarcinoma (ICC) or perihilar cholangiocarcinoma (PHC) had tumor samples assessed for FGFR2 fusions or rearrangements by a break‐apart fluorescence in situ hybridization probe kit analyzed at a central laboratory; multivariate analyses using a logistic regression model were conducted to investigate the relationship between FGFR2 fusions or rearrangements and patients' baseline characteristics; two cut‐off values ( p ‐values of 0.15 and 0.05) were used. Results: Of the 453 patients observed, 25 (5.5%) had FGFR2 fusions or rearrangements, corresponding with 7.4% (23/306) of patients with ICC and 1.4% (2/144) of patients with PHC. Of 426 evaluable patients, FGFR2 fusions or rearrangements were associated with hepatitis C antibodies (odds ratio [OR] 6.901; p < 0.05); patients who had PHC versus ICC (OR 0.273; p < 0.05) or were men (OR 0.431; p < 0.15) were less likely to have FGFR2 fusions or rearrangements. Of 252 evaluable patients with ICC, FGFR2 fusions or rearrangements were associated with hepatitis C antibodies (OR 9.500; p < 0.05); patients who were men (OR 0.419; p < 0.05) or were aged ≥65 years (OR 0.406; p < 0.15) were less likely to have FGFR2 fusions or rearrangements. Conclusions: This large observational study helps to characterize factors associated with FGFR2 fusions or rearrangements. Further study is warranted to explore differences in prevalence among different geographic populations and patients with PHC.