The depth of invasion and the extent of nodal and distant metastasis at the time of diagnosis remain the most powerful prognostic indicators for gastric cancer. Local invasion into the duodenum, pancreas, and retroperitoneum is also characteristic. When possible, surgical resection remains the preferred treatment for gastric adenocarcinoma. After surgical resection, the 5-year survival rate for early gastric cancer can exceed 90%, even if lymph node metastases are present. By contrast, the 5-year survival rate for advanced gastric cancer remains below 20%, in large part because current chemotherapy regimens are have limited impact. This is changing slowly with individualized therapies. For example, patients whose tumors over-express the epidermal growth factor receptor HER2 benefit from agents that inhibit HER2 signaling. Nevertheless, most gastric cancers are discovered at advanced stage in the United States, and the overall 5-year survival rate is less than 30%.
Although extranodal lymphomas can arise in virtually any tissue, they do so most commonly in the gastrointestinal tract, particularly the stomach. In allogeneic hematopoietic stem cell and organ transplant recipients, the bowel also is the most frequent site for Epstein-Barr virus–positive B cell lymphoproliferations. Nearly 5% of all gastric malignancies are primary lymphomas, the most common of which are indolent extranodal marginal zone B-cell lymphomas. In the gut, these tumors often are referred to as lymphomas of MALT, or MALTomas. This entity and the second most common primary lymphoma of the gut, diffuse large B cell lymphoma, are discussed in Chapter 12.
Neuroendocrine tumors, also referred to as carcinoid tumors, arise from neuroendocrine organs (e.g., the endocrine pancreas) and neuroendocrine-differentiated gastrointestinal epithelia (e.g., G cells). A majority of these tumors are found in the gastrointestinal tract, and more than 40% occur in the small intestine. The tracheobronchial tree and lungs are the next most commonly involved sites. Gastric neuroendocrine tumors may be associated with endocrine cell hyperplasia, chronic atrophic gastritis, and Zollinger-Ellison syndrome. These tumors were called “carcinoid” because they are slower growing than carcinomas. The most current WHO classification describes these as low-or intermediate-grade neuroendocrine tumors. High-grade neuroendocrine tumors, termed neuroendocrine carcinoma, resemble small cell carcinoma of the lung (Chapter 13) and, in the gastrointestinal tract, are most common in the jejunum.
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Fig. 15.17 Gastrointestinalcarcinoidtumor(neuroendocrinetumor).(A)Carcinoidtumorsoftenformasubmucosalnodulecomposedoftumorcellsembeddedindensefibroustissue.(B)Highmagnificationshowstheblandcytologythattypifiesneuroendocrinetumors.Thechromatintexture,withfineandcoarseclumps,frequentlyassumesa“salt-and-pepper”pattern.Despitetheirinnocuousappearance,tumorscanbeaggressive.
Fig.15.17A ).Thetumorsareyellowortaninappearanceandelicitanintensedesmoplasticreactionthatmaycausekinkingofthebowelandobstruction.Onhistologicexamination,neuroendocrinetumorsarecomposedofislands,trabeculae,strands,glands,orsheetsofuniformcellswithscant,pinkgranularcytoplasmandaround-to-ovalstipplednucleus(
Fig.15.17B