“…Major criteria are the depth of tumor invasion to the muscularis propria and beyond [2,11,16,17,20,21,24,32,33,[35][36][37][38]40,45,49], angioinvasion and lymphatic invasion [35,36,39,43,49], cellular atypia with hyperchromatic nuclei and high nuclear to cytoplasmic ratio [9,36,49], areas of focal necrosis [9,39,43,49], and a high mitotic index (number of mitoses per 10 high power fields) [9,36,39,43,49]. It is a well-recognized clinical experience that among patients with metastatic carcinoid tumors, some have an indolent clinical course with survival of several years, whereas others experience an aggressively malignant course with short survival.…”