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Background: Gastrointestinal subepithelial lesions (SELs) range from benign to malignant. Endoscopic ultrasound (EUS)-guided fine-needle biopsy (EUS-FNB) is used widely for pathological diagnosis of SELs. Early diagnosis and treatment are important because all Gastrointestinal stromal tumors (GISTs) have some degree of malignant potential. Diagnosing SELs with EUS-FNB is more difficult than diagnosing other tumors because an accurate diagnosis of GIST requires a sufficient tissue sample for immunostaining, which is part of the diagnostic protocol. Moreover, EUS-FNB is less accurate for diagnosis based on samples from SELs measuring ≤ 2 cm. However, our retrospective study showed that more than 50% of patients with SELs ≤ 2 cm were diagnosed as GIST. Therefore, EUS-FNB needles are required with adequate sampling in SELs measuring ≤ 2 cm. Previously, we conducted a retrospective single-center study of SELs measuring ≤ 2 cm, and reported that EUS-FNB with a Fork-tip needle was superior to that with a Franseen needle in that the former acquires sufficient sample. This multicenter comparative open-label superiority study is designed to verify whether a 22G Fork-tip needle is superior to a 22G Franseen needle with respect to sample acquisition., Methods/design: Present study will randomly assign for 110 patients (55 in the Fork-tip needle group and 55 in the Franseen needle group) with SELs measuring ≤ 2 cm, all of whom are managed at one of the 10 participating endoscopic centers. The primary endpoint evaluates the superiority of a 22G Fork-tip needle over a 22G Franseen needle for collection of an adequate tissue specimen at the first puncture. The secondary endpoints compare successful puncture rate, procedure completion rate, number of adverse events, diagnostic suitability of the first puncture specimen for GIST, and the number of punctures required until adequate specimen collection., Discussion: The outcomes may provide insight into the optimal needle choice for diagnosis of SELs ≤ 2 cm, thereby aiding development of practice guidelines. Present study is expected to promote early definitive diagnosis of GISTs, thereby increasing the number of cases that can receive curative treatment and improving prognosis., Trial Registration: Japan Registry of Clinical Trials (JRCT; trial registration: jRCTs052230144). Registered December 13, 2023. (URL; https://jrct.niph.go.jp/re/reports/detail/76858 )., Competing Interests: Declarations. Ethics approval and consent to participate: This protocol has been approved by Wakayama medical University Certified Review Board (approval number. W-59). The results will be submitted to peer-reviewed journals and will be presented at international conferences. Informed consent will be obtained from all patients by investigator. Consent for publication: Not applicable. Competing interests: The authors declare that they have no competing interests., (© 2024. The Author(s).)

Objectives: Early gastric cancer endoscopic resection (ER) is prominent in Japan. However, evidence regarding ER of gastric submucosal tumors (SMT) is limited. This prospective multicenter phase II study investigated the efficacy and safety of endoscopic full-thickness resection (EFTR) for gastric SMT., Methods: Endoscopic full-thickness resection indication for gastric SMT was 11-30 mm, histologically proven or clinically suspicious (irregular margin, increasing size, or internal heterogeneity) gastrointestinal stromal tumors (GIST), with no ulceration and intraluminal growth type. The primary end-point was the complete ER (ER0) rate, with a sample size of 42., Results: We enrolled 46 patients with 46 lesions between September 2020 and May 2023 at seven Japanese institutions. The mean ± SD (range) endoscopic tumor size was 18.8 ± 4.5 (11-28) mm. The tumor resection and defect closure times were 54 ± 26 (22-125) min and 33 ± 28 (12-186) min, respectively. A 100% ER0 was achieved in all 46 patients. The EFTR procedure was accomplished in all patients without surgical intervention. One patient had delayed perforation and was managed endoscopically. GIST accounted for 76% (n = 35) of the cases. R0, R1, and RX rates were 33 (77%), 3 (6.5%), and 7 (15%), respectively., Conclusion: Endoscopic full-thickness resection for gastric SMT of 11-30 mm is efficacious. It warrants further validation in a large-scale cohort study to determine the long-term outcome of this treatment for patients with gastric GIST., (© 2023 Japan Gastroenterological Endoscopy Society.)

Pimitespib (TAS-116) is the first heat shock protein 90 (HSP90) inhibitor approved in Japan, and it is indicated for the treatment of gastrointestinal stromal tumors (GIST) that have progressed after treatment with imatinib, sunitinib and regorafenib. This review describes the preclinical and clinical research with pimitespib, including its mechanism of action, pharmacokinetics, clinical antitumour activity and safety. In a phase III study, pimitespib significantly prolonged progression-free survival compared with placebo (median 2.8 vs 1.4 months; hazard ratio 0.51; 95% CI 0.30-0.87; p = 0.006). Common treatment-related adverse events were diarrhoea, decreased appetite, increase in serum creatinine, malaise, nausea and eye disorders. The efficacy and safety of pimitespib are being investigated in other tumour types and in combination with other anticancer therapies.

Tyrosine kinase inhibitors (TKIs) improve the prognosis of patients with gastrointestinal stromal tumors (GISTs). We conducted a retrospective cohort study using cancer registries linked with health utilization data in Japan and Taiwan to assess TKI usage in older and non-older patients. Patients diagnosed with GIST (2012-2014) were categorized into the following: adjuvant and advanced/metastatic settings. The duration and patterns of imatinib therapy were compared between the older (aged ≥ 75 years) and non-older (< 75 years) groups. We included 232 Japanese and 492 Taiwanese patients in the adjuvant setting, and 235 Japanese and 401 Taiwanese patients in the advanced/metastatic setting. Older patients had higher proportions of starting with lower doses (< 400 mg/day) than the non-older patients (adjuvant: 22.5% vs. 4.3% [Japan]; 22.5% vs. 10.9% [Taiwan]; advanced/metastatic: 29.6% vs. 7.2% [Japan]; 32.6% vs. 8.1% [Taiwan]; all p < 0.01). The median time to stop imatinib was shorter in the older than in the non-older patients (adjuvant: 301 vs. 975 days [Japan], 366 vs. 1028 days [Taiwan]; advanced/metastatic: 423 vs. 542 days [Japan]; 366.5 vs. 837 days [Taiwan]). More older patients with GIST tended to have TKIs at a lower initial dose and a shorter imatinib duration than the non-older patients., (© 2022. The Author(s).)

Background: Regorafenib is an oral multi-kinase inhibitor that has been established as third-line treatment for patients after the failure of imatinib and sunitinib. However, since clinical data of regorafenib in the Japanese population are still lacking, the management of regorafenib is mainly based on the clinical experience of each oncologist. The aim of this study was to evaluate the efficacy and safety of regorafenib in a Japanese population., Methods: Thirty-three patients treated with regorafenib for metastatic and recurrent gastrointestinal stromal tumors were retrospectively enrolled. This study investigated the anti-tumor effect, including overall survival, progression-free survival, and safety, which was evaluated based on the incidence of adverse events., Results: The median overall survival of patients treated with regorafenib was 23.8 months and the 1-year overall survival rate was 80.0%, the median progression-free survival was 7.1 months and the 1-year progression-free survival rate was 40.2%. The responses to regorafenib were partial response in 3 cases (9.1%), stable disease in 17 (51.5%), progressive disease in 10 (30.3%), and non-evaluable in 3 (9.1%). The disease control rate was 54.0%. Treatment-related adverse events were reported in all patients, with the most common being hand-foot syndrome (72.7%), followed by liver damage (36.4%) and diarrhea (27.3%), and six patients (20.0%) were discontinued due to adverse events., Conclusion: This is the first report of Japanese patients with gastrointestinal stromal tumors treated with regorafenib. Regorafenib showed efficacy and a manageable safety profile in Japanese patients with advanced gastrointestinal stromal tumors, which was comparable with previous studies., (© 2022. The Author(s) under exclusive licence to Japan Society of Clinical Oncology.)

Background: Complete surgical resection is the only treatment for resectable gastrointestinal stromal tumors (GISTs). Three-year adjuvant chemotherapy (AC) is recommended for patients with high-risk GISTs. However, there are scarce data on this topic in Japan. We aimed to study the efficacy and safety of AC in Japanese patients with high-risk GISTs., Methods: Patients with high-risk GISTs who received complete resections during 1992-2019 in our hospitals were included in this retrospective study. We evaluated patients' treatments with or without AC, completion rates, adverse events (AEs), recurrence-free survival (RFS), and overall survival (OS)., Results: Overall, 89 patients categorized as high risk were enrolled in this study. Fifty-five patients received AC (AC group), and 34 patients did not receive AC (control group). Twenty-three (41.8%) patients experienced Common Terminology Criteria for Adverse Events Grade 2 or higher AEs. At a median follow-up of 61.6 months, 41 (74.5%) patients completed the planned treatment (including six patients with ongoing treatment), whereas 14 (25.4%) patients did not complete the treatment owing to the development of AEs (nine patients), patients' request (three patients), recurrence (one patient), and mutational analysis (one patient). Comparing the data between the treatment and control groups, the RFS rate was significantly better for the AC group (P < 0.001). However, there was no significant difference in the OS rate between the two groups., Conclusion: Postoperative AC was well tolerated by Japanese patients at an acceptable rate, and its use may reduce the risk of recurrence in patients with high-risk GISTs., (© 2022. The Author(s) under exclusive licence to Japan Society of Clinical Oncology.)

Background: Gastric subepithelial lesions, including gastrointestinal stromal tumors, are often found during routine gastroscopy. While endoscopic ultrasound-guided fine-needle aspiration biopsy (EUS-FNAB) has been the gold standard for diagnosing gastric subepithelial lesions, alternative open biopsy procedures, such as mucosal incision-assisted biopsy (MIAB) has been reported useful. The aim of this study is to evaluate the efficacy of MIAB for the diagnosis of gastric SELs compared with EUS-FNAB., Methods: We retrospectively analyzed medical records of 177 consecutive patients with gastric SELs who underwent either MIAB or EUS-FNAB at five hospitals in Japan between January 2010 and January 2018. Diagnostic yield, procedural time, and adverse event rates for the two procedures were evaluated before and after propensity-score matching., Results: No major procedure-related adverse events were observed in either group. Both procedures yielded highly-accurate diagnoses once large enough samples were obtained; however, such successful sampling was more often accomplished by MIAB than by EUS-FNAB, especially for small SELs. As a result, MIAB provided better diagnostic yields for SELs smaller than 20-mm diameter. The diagnostic yields of both procedures were comparable for SELs larger than 20-mm diameter; however, MIAB required significantly longer procedural time (approximately 13 min) compared with EUS-FNAB., Conclusions: Although MIAB required longer procedural time, it outperformed EUS-FNAB when diagnosing gastric SELs smaller than 20-mm diameter.

Aim: We evaluated the efficacy and safety of TAS-116, a novel class of an orally active selective inhibitor of heat shock protein 90, in patients with advanced gastrointestinal stromal tumour (GIST) after failure of three or more lines of standard treatment with imatinib, sunitinib and regorafenib., Methods: In this single-arm phase II study, patients received 160 mg/day oral TAS-116 for five consecutive days, followed by a 2-day rest. The primary end-point was centrally assessed progression-free survival (PFS). The secondary end-points were objective response rate, disease control rate, overall survival (OS), metabolic response rate, safety, pharmacokinetics and pharmacogenomics., Results: Forty-one patients were enrolled in Japan, and 40 patients underwent efficacy and safety evaluation. At the cut-off date, the median PFS was 4.4 months (95% confidence interval [CI], 2.8-6.0) and 12-week progression-free rate was 73.4% (95% CI, 58.1-88.7). Thirty-four patients (85.0%) had stable disease for ≥ 6 weeks. The median OS was 11.5 months (95% CI, 7.0-not reached). All patients experienced at least one treatment-related adverse event (AE), including diarrhoea (80.0%), decreased appetite (45.0%) and increase in blood creatinine level (42.5%). Grade ≥3 AEs and treatment-related grade ≥3 AEs occurred in 23 (57.5%) and 21 (52.5%) patients, respectively. All AEs resolved after dose modification, and no TAS-116-related AEs led to treatment discontinuation., Conclusion: TAS-116 showed significant activity in advanced GIST refractory to standard treatment. Further development of TAS-116 is warranted., Trial Registration: JapicCTI-163182., (Copyright © 2019 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

HSP90 is involved in stability and function of cancer-related proteins. This study was conducted to define the MTD, safety, pharmacokinetics, pharmacodynamics, and preliminary antitumor efficacy of TAS-116, a novel class, orally available, highly selective inhibitor of HSP90. Patients with advanced solid tumors received TAS-116 orally once daily (QD, step 1) or every other day (QOD, step 2) in 21-day cycles. Each step comprised a dose escalation phase to determine MTD and an expansion phase at the MTD. In the dose escalation phase, an accelerated dose-titration design and a "3+3" design were used. Sixty-one patients were enrolled in Japan and the United Kingdom. MTD was determined to be 107.5 mg/m 2 /day for QD, and 210.7 mg/m 2 /day for QOD. In the expansion phase of step 1, TAS-116 was administered 5 days on/2 days off per week (QD × 5). The most common treatment-related adverse events included gastrointestinal disorders, creatinine increases, AST increases, ALT increases, and eye disorders. Eye disorders have been reported with HSP90 inhibitors; however, those observed with TAS-116 in the expansion phases were limited to grade 1. The systemic exposure of TAS-116 increased dose-proportionally with QD and QOD regimens. Two patients with non-small cell lung cancer and one patient with gastrointestinal stromal tumor (GIST) achieved a confirmed partial response. TAS-116 had an acceptable safety profile with some antitumor activity, supporting further development of this HSP90 inhibitor.This is a result from a first-in-human study, in which the HSP90 inhibitor TAS-116 demonstrated preliminary antitumor efficacy in patients with advanced solid tumors, including those with heavily pretreated GIST., (©2019 American Association for Cancer Research.)

The aim of this study was to evaluate the treatment and prognosis of gastric gastrointestinal stromal tumors (GISTs) according to the 7th UICC/AJCC tumor-node-metastasis (TNM) system and the modified National Institutes of Health (NIH) risk classification. The study cohort consisted of 1057 patients with gastric GIST who underwent surgery between January 2000 and December 2007 from 13 institutions in Korea and 2 in Japan. Clinicopathologic characteristics, surgical outcomes, recurrence, and 5-year recurrence-free survival were evaluated.The mean age of the patients was 58.6 years. Thirty patients (2.8%) had distant metastasis preoperatively. Median tumor size was 4.0 cm. Complete resection (R0 resection) was achieved in 1018 patients (96.3%). Eighty-six patients (8.1%) had postoperative complications, and 2 patients (0.2%) died within 30 days after surgery. According to the 7th UICC/AJCC TNM system, 5-year recurrence-free survival rates were 95% to 99% in stage I, 94.1% in stage II, 74.1% in stage IIIA, 48.6% in stage IIIB, and 50.0% in stage IV patients. On survival analysis of high-risk patients according to the TNM system, the 5-year recurrence-free survival rates were 91.6% in stage II, 74.1% in stage IIIA, and 48.6% in stage IIIB patients. Independent factors of recurrence following surgery for gastric GIST were gender, tumor size, mitotic count, and radicality on multivariate analysis.The treatment outcome and prognosis of gastric GIST in Korea and Japan seem more favorable compared to those in Western countries. Compared to the modified NIH risk classification, the 7th UICC/AJCC TNM system is more reflective of the 5-year recurrence-free survival of patients with gastric GIST.

Background: Gastrointestinal stromal tumors (GISTs) of the stomach are found incidentally during gastric cancer screening in Japan. This study investigated whether the Japanese gastric cancer screening system helps to improve treatment outcomes in gastric GIST based on an analysis of the GIST registry conducted by the Kinki GIST Study Group., Methods: The registry was designed to collect data on background characteristics, treatment methods, pathologic characteristics, and prognosis of GIST from January 2003 through December 2007 at 40 participating institutions., Results: The study enrolled 672 GIST patients, 482 of whom had gastric GIST. According to the modified National Institutes of Health consensus criteria, 22.6 % of the patients were classified as high risk for recurrence, 18.5 % as intermediate risk, 35.9 % as low risk, and 13.9 % as very low risk. After exclusion of the patients inevaluable for treatment outcome, the study included 137 symptomatic patients (symptomatic group) and 147 asymptomatic patients (asymptomatic group). The diagnosis of the asymptomatic patients was determined through gastric cancer screening. The median tumor size in the asymptomatic group was significantly smaller than in the symptomatic group (3.5 vs. 5.3 cm; P < 0.0001). The 5-year recurrence-free survival rate in the asymptomatic high-risk patients (72.4 %) was lower than in their symptomatic counterparts (46.3 %) (P = 0.017). More patients in the asymptomatic group underwent laparoscopic surgery (42.2 vs. 27.2 %; P = 0.0081)., Conclusions: By identifying asymptomatic patients, the Japanese gastric cancer screening system contributes to early detection of gastric GIST and favorable treatment outcomes.

Background: Imatinib mesylate, a small-molecule tyrosine kinase inhibitor, is currently used for adjuvant therapy of patients who have undergone resection of high-risk gastrointestinal stromal tumors (GISTs). There are no data concerning the efficacy and safety of postoperative adjuvant therapy with imatinib for Japanese or East Asian patients with GIST., Methods: A single-arm, open-label, multicenter trial was conducted in 17 hospitals in Japan. The eligibility criteria included histologically proven primary high-risk GISTs with macroscopic complete resection. Patients were treated with imatinib at a dose of 400 mg/day for 1 year after surgery. The primary endpoint was recurrence-free survival as assessed by Kaplan-Meier analysis. The secondary endpoints were overall survival and safety. This study was registered with ClinicalTrials.gov, number NCT00171977., Results: A total of 64 patients were enrolled between September 2004 and July 2006. The median age of the patients was 59.5 years. Forty-nine (76.6%) patients completed the 1-year treatment, whereas 15 (23.4%) patients did not complete the treatment owing to recurrence, toxicities, and consent withdrawal. At the median follow-up period of 109 weeks, 20 patients had recurrence. The 3-year recurrence rate was 42.7% (95% confidence interval 29.2-56.3%), which exceeded the expected recurrence rate in this trial. The recurrence-free and overall survival rates at 2 years were 71.1 and 93.7%, respectively. The most frequent adverse drug reaction of any grade was eyelid edema (48.4%), followed by neutropenia (40.6%), leukopenia (39.1%), nausea (39.1%), rash (37.5%), and peripheral edema (37.5%), most of which were mild and manageable., Conclusions: Adjuvant therapy with imatinib at 400 mg/day for 1 year is well tolerated by Japanese patients and possibly reduces the risk of early recurrence of high-risk GISTs.

Objective: Limited data are available concerning long-term results of imatinib therapy in patients with advanced gastrointestinal stromal tumors. We aimed to clarify the long-term outcomes of imatinib therapy in Japanese patients with advanced gastrointestinal stromal tumors., Methods: A prospective, observational study of imatinib therapy for unresectable and metastatic gastrointestinal stromal tumors was conducted in our institution. Imatinib was initiated at a dose of 400 mg daily and continued until disease progression. Safety, efficacy and long-term tolerability and survival were evaluated in an intent-to-treat population. The median follow-up period in this study was 68 months., Results: Seventy patients were enrolled between December 2001 and December 2009. Treatment-related Grade 3/4 adverse events occurred in 49 patients (70.0%). Although 14 patients required adverse effect management with hospitalization, only 5 patients (7.1%) withdrew from the treatment owing to imatinib intolerance. The tumor response and clinical benefit rates were 61.4 and 85.7%, respectively. Thirty-seven patients (52.9%) maintained the treatment at 400 mg daily imatinib, whereas 33 patients (47.1%) had their dose reduced to 300 mg daily or less. The overall survival rate at 5 years was 60.9% and the median survival time was 70 months. The median progression-free survival time of all the 70 enrolled patients was 30 months. Seven patients (10.0%) suffered from second malignancies, including three patients with genitourinary carcinomas., Conclusions: Despite the need for dose reduction, the long-term results of imatinib therapy for advanced gastrointestinal stromal tumors were good in Japanese patients. Physicians should pay attention to the occurrence of second malignancies during imatinib therapy for gastrointestinal stromal tumor patients.

The author herein reports histopathologic features of 31 surgical cases of gastrointestinal stromal tumor (GIST) of the digestive organs. The 31 cases of GIST were diagnosed in our pathology laboratory. They consisted of 24 cases of gastric GIST, 1 case of hepatic GIST, 1 case of small intestinal GIST, 4 cases of colon GIST, and 1 case of rectal GIST. The age of the patients ranged from 56 year to 84 years with a mean of 71 years. Male to female ratio was 21:10. The presenting symptoms were gastrointestinal bleeding in 13 cases, abdominal pain and discomfort in 13 cases, and asymptomatic in 5 cases. Endoscopy and imaging modalities including US, CT and MRI were useful to detect the tumors in all cases, and biopsies confirmed the GIST diagnosis in 21 cases. The size of GIST ranged from 1 cm to 12 cm with a mean of 4.3 cm. Grossly, 23 cases were submucosal tumors, 6 serosa-side tumors, 1 solid tumor in the liver, and 1 rectal polyp. Histologically, 28 cases were of spindle cell type and 3 of epithelioid type. According to mitotic counts and tumor size, the malignant risk was very low in 4 cases, low in 14 cases, intermediate in 9 cases, and high in 4 cases. Immunohistochemically, all cases were positive for KIT and vimentin, 30 cases for CD34, and 4 cases for alpha-smooth muscle actin. None were positive for desmin and S100 protein. Ki-67 labeling ranged from 2% to 18%. P53 protein was negative in all cases. PDGFRA was positive in 20 cases among 24 cases examined. Genetic analysis using PCR-direct sequencing method was performed in 5 GISTs; all the 5 GISTs showed point mutations or deletions in KIT gene, but did not in PDGFRA gene. The 5 cases of GIST were positive for PDGFRA protein, suggesting that PDGFRA overexpression is not associated with PDGFRA gene mutations. Four of the 31 cases showed metastases. The chemotherapy was imatinib mesylate in 6 cases, and none in 25 cases. Four cases of high risk died of GIST, and 27 cases are alive now without tumors.

Although imatinib showed high activity for advanced gastrointestinal stromal tumor (GIST) and improved the prognosis of GIST patients, resistance to the drug appears with prolonged use. Mechanisms of acquired resistance are still under investigation. In the present study, we carried out histologic and genetic analysis of 45 secondary resistant lesions obtained from 25 Japanese GIST patients treated with imatinib. All resistant lesions showed viable tumor cells expressing KIT protein, whereas imatinib-sensitive lesions did not. All pre-imatinib samples have KIT mutations either in exon 9 (n = 3) or exon 11 (n = 22), identified in the KIT gene of corresponding resistant tumors. In addition to primary mutations, 33 out of 45 tumors (73%) showed secondary KIT mutations in the kinase domain of the KIT gene. Secondary mutations are missense mutations and are mostly located in the kinase domains of the same allele to the primary mutations (cis-position). Resistant lesions showed monoclonal development of tumor cells. Taken together, additional cis-positioned mutations in the kinase domains are a major cause of secondary resistance to imatinib in Japanese GIST patients.

Purpose: Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract arising from Cajal's cells and expressing c-kit. In a consensus report, the clinical behavior of GISTs was categorized into risk classes according to the tumor size and mitotic count. We analyzed the risk categories based on GIST patients who underwent a surgical resection at our institute during a period of 15 years., Methods: We evaluated the risk categories of GISTs and analyzed the outcome and risk categories retrospectively. We presented the MIB-1 score of the tumor instead of mitotic counts for the evaluation of cellular growth because of inaccuracies regarding the mitotic counts., Results: Patients were classified into 4 cases of very low risk, 11 of low risk, 8 of intermediate risk, and 5 of high risk. Four high-risk patients showed recurrence as either liver metastasis or peritoneal dissemination. In addition, local recurrence occurred in one low-risk and one intermediate-risk patient each., Conclusion: Our cases confirmed the correlation between the risk categories and the prognosis. A complete resection with sufficient margin must be confirmed even in low-risk cases to prevent local recurrence. Since high-risk patients showed poor prognosis, the adjuvant treatment with chemotherapeutic regimens must therefore be further studied for high-risk patients.

Gastrointestinal stromal tumors (GISTs) are rare mesenchymal neoplasms with an annual incidence of approximately 10 to 20 per 1 million cases. Although pathologists have often observed incidental small GISTs in the stomach resected from patients with gastric cancer, no report on the real incidence of gastric GISTs is available. In this study, 100 whole stomachs resected from patients with gastric cancer were sectioned at 5-mm intervals and hematoxylin and eosin-stained slides (a mean of 130 slides for each case) were examined for microscopic GISTs. KIT (CD117), CD34, and desmin expression of the incidental tumors was evaluated by immunohistochemistry, and genomic DNA extracted from formalin-fixed and paraffin-embedded tumor tissues was analyzed for c-kit gene mutations in exon 11. In 35 of the 100 whole stomachs, we found 50 microscopic GISTs, all of which were positive for KIT and/or CD34 and negative for desmin. Most microscopic GISTs (45/50, 90%) were located in the upper stomach. Two of the 25 (8%) microscopic GISTs had c-kit gene mutations. Fifty-one leiomyomas with positive expression for desmin were observed in 28 of the 100 stomachs. Both leiomyomas and GISTs were found in 12 stomachs. These results indicate that microscopic GISTs are common in the upper portion of the stomach. Considering the annual incidence of clinical GISTs, only few microscopic GISTs may grow into a clinical size with malignant potential. Further studies are required to clarify the genetic events responsible for the transformation of microscopic GISTs to clinical GISTs.

Imatinib mesylate is the first and only effective drug for the treatment of gastrointestinal stromal tumor at present. Mutated exon 11 of the KIT receptor is essential for the pathogenesis and response to imatinib mesylate of gastrointestinal stromal tumor; the efficacy rate (complete response+partial response) of imatinib mesylate is 53.8%, and the disease-control rate (complete response+partial response+stable disease) is 84%. Almost 90% of patients experienced non-hematological and hematological adverse effects, which were tolerable, in particular at a daily dose of 400 mg imatinib mesylate, which warranted response induction for half of the patients, and is the dose approved by Japanese medical insurance. Clinical trials suggest that an increased dose of imatinib mesylate would be beneficial, and that the interruption of imatinib treatment might result in disease progression even after a partial response. Tentative Japanese guidelines for the diagnosis and therapy of gastrointestinal stromal tumors are being prepared by the Gastrointestinal Stromal Tumor Committee of the Japan Society of Clinical Oncology, and are presented here for critical comments by colleagues.

Immunostaining depending on antigen-antibody specificity is the commonest approach for determining the localization of specific antigens in tissue sections. This procedure is applicable not only with frozen or specially fixed samples, but also has proved reliable with formalin-fixed paraffin-embedded tissue sections through improvement of antigen-retrieval. Immunostaining is thus firmly established as a tool for diagnostic pathology and in our institute multiple antibodies are applied for 13-15% of the cases examined, as well as H and E staining. With the standard approach, approximately 3 h is necessary from the beginning of deparaffinization till covering sections with the Envision system. We utilized intermittent microwave irradiation for 10 min during hybridization with primary and secondary antibodies in a special moist-chamber, to achieve all immunostaining steps within 1 h in 178 primary antibodies frequently used for diagnostic pathology. According to our 5 years experience, such microwave irradiation not only obtained significant specific staining for enhancing the specificity of antigen-antibody reactions, but also inhibited nonspecific binding. We present herein the details of the methodology and recommendations for its application with particular primary antibodies. This method can contribute to savings in time and energy, allowing pathologists to rapidly obtain diagnostic information.