Diagnostic and treatment strategies for gastrointestinal stromal tumors (GISTs) have evolved greatly since the introduction of molecularly targeted therapies. Although several clinical practice guidelines are extant, such as those published by the National Comprehensive Cancer Network and the European Society of Medical Oncology, it is not clear as to whether these are appropriate for clinical practice in Japan. Therefore, clinical practice guidelines for the optimal diagnosis and treatment of GIST tailored for the Japanese situation have often been requested. For this reason, the Japanese Clinical Practice Guideline for GIST was proposed by the GIST Guideline Subcommittee, with the official approval of the Clinical Practice Guidelines Committee for Cancer of the Japan Society of Clinical Oncology (JSCO), and was published after assessment by the Guideline Evaluation Committee of JSCO. The GIST Guideline Subcommittee consists of members from JSCO, the Japanese Gastric Cancer Association (JGCA), and the Japanese Study Group on GIST, with the official approval of these organizations. The GIST Guideline Subcommittee is not influenced by any other organizations or third parties. Revision of the guideline may be done periodically, with the approval of the GIST Guideline Subcommittee, either every 3 years or when important new evidence that might alter the optimal diagnosis and treatment of GIST emerges. Here we present the English version of the Japanese Clinical Practice Guideline for GIST prepared by the GIST Guideline Subcommittee.

Primary retroperitoneal neoplasms are a rare but diverse group of benign and malignant tumors that arise within the retroperitoneal space but outside the major organs in this space. Although computed tomography and magnetic resonance imaging can demonstrate important characteristics of these tumors, diagnosis is often challenging for radiologists. Diagnostic challenges include precise localization of the lesion, determination of the extent of invasion, and characterization of the specific pathologic type. The first step is to determine whether the tumor is located within the retroperitoneal space. Displacement of normal anatomic structures of the retroperitoneum is helpful in this regard. For tumors that are located within the retroperitoneum, the next step is to identify the organ of origin. Specific signs, including the "beak sign," the "embedded organ sign," and the "phantom (invisible) organ sign," are useful for this purpose. When there is no definite sign that suggests the organ of origin, the diagnosis of a primary retroperitoneal tumor becomes likely. Awareness of specific patterns of spread, specific tumor components, and tumor vascularity help in further narrowing the differential diagnosis. Attention to these diagnostic clues is essential in making an accurate radiologic diagnosis of primary retroperitoneal tumors and in obtaining clinically significant information.

The histopathologic grade of HCC had no correlation with the ADC, but HCC tumors tended to show a higher signal on DWI as the histopathologic grade rose. However, predicting the correct histopathologic grade of each HCC before surgery on the basis of DWI findings was difficult because of the large overlap among histopathologic grades.

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Incremental dynamic computed tomography (CT) was prospectively performed in 89 patients with gastric tumors (78 gastric cancers, five malignant lymphomas, and six submucosal tumors) after the intake of 400 mL of water, and findings were compared with those obtained at pathologic examination. Dynamic CT of healthy control subjects (15 patients without gastric lesions) showed the gastric wall as a two- or three-layered structure (multilayered pattern): a markedly enhanced inner layer; an intermediate layer of low attenuation; and (sometimes) an outer layer of slightly high attenuation, which corresponded histologically to the mucosal layer, submucosal layer, and muscular-serosal layer, respectively. In 68 lesions that were removed at surgery, the detectability of early and advanced gastric cancers and the accuracy of classification of gross appearance and serosal invasion as determined with CT were 53%, 92%, 80%, and 80%, respectively. All detected advanced gastric cancers were seen as enhanced areas with the destruction of the multilayered pattern. Differentiation between infiltrating gastric cancer (n = 5) and malignant lymphoma (n = 5) was successful. Five of six submucosal tumors were demonstrated as having an overlying intact mucosal layer.