Fig. 1

Endoscopic images showing the gastric mucosa at various levels of magnification. a Bleeding associated with an irregular, protruding lesion observed on the rear wall of the lesser curvature in the body of the stomach. b Segmental gastrectomy specimen. A 41 × 29 × 18 mm³ protruding lesion is observed. c The cross-section shows a grayish-white tumor with growth mainly on the mucous membranous side, partly composed of cystoid portions and a translucent cartilage-like matrix (indicated by the red arrow). d Low magnification (× 0.4) imaging indicating carcinosarcoma invasion limited to the submucosa. Cartilaginous tissue is visible indicated by the red arrow. e Magnified imaging (× 20 magnification) indicating an adenocarcinomatous component with tubular and papillary growth mixed with a sarcomatous component (scale bar 200 μm). f Higher magnification (× 200) imaging, indicating an acidophilic and cylindrical adenocarcinomatous component as well as a sarcomatous component with atypical spindle cell and atypical round cell proliferation with a high N/C ratio (scale bar 50 μm). g Magnified imaging (× 100) of a region showing chondrogenesis. Dyskaryosis is visible in chondrocyte-like cells (scale bar 100 μm)