Fig. 1

Pathologic findings of collision tumor accompanied with neuroendocrine carcinoma and adenocarcinoma. a Red circle: adenocarcinoma, well-differentiated area. Tumor cells forming gland and showing infiltrative growth. Under area: solid tumor cell nest (H&E stain, ×40). b High power view of adenocarcinoma area (H&E stain, ×400). Atypical epithelial cells forming gland. c High power view of solid nest area (H&E stain, ×400). The tumor cell showing typical “salt and pepper” chromatin pattern which is compatible with neuroendocrine tumor cells. They are positive for neuroendocrine marker, synaptophysin and chromogranin in immunohistochemistry staining. d The neuroendocrine tumor area showing increased mitosis (red arrow), and increased Ki-67 index (about 70%) (H&E stain, ×400)