Antigens, CD34/analysis; Antigens, CD34/immunology; Duodenal Neoplasms/immunology; Duodenal Neoplasms/pathology; Gene Expression Regulation, Neoplastic/immunology; Jejunal Neoplasms/immunology; Jejunal Neoplasms/pathology; Mesenchymoma/immunology; Mesenchymoma/pathology; Proto-Oncogene Proteins c-kit/analysis; Proto-Oncogene Proteins c-kit/immunology; Smooth Muscle Tumor/immunology; Smooth Muscle Tumor/pathology; Stomach Neoplasms/immunology; Stomach Neoplasms/pathology; Adult; Aged; Aged, 80 and over; Coiled Bodies/immunology; Duodenal Neoplasms/mortality; Duodenal Neoplasms/surgery; Female; Follow-Up Studies; Gastrectomy; Humans; Immunohistochemistry; Immunophenotyping; Jejunal Neoplasms/mortality; Jejunal Neoplasms/surgery; Male; Mesenchymoma/mortality; Mesenchymoma/surgery; Microscopy, Electron; Middle Aged; Pancreaticoduodenectomy; Predictive Value of Tests; Prognosis; Smooth Muscle Tumor/mortality; Smooth Muscle Tumor/surgery; Stomach Neoplasms/mortality; Stomach Neoplasms/surgery; Survival Analysis