Fig. 1

Typical Elastic Lamina Invasion and Definition of pT3 Classification. H&E and EVG stained micrographs of the same case were shown in a vertical row. Arrow heads: elastic lamina (EL); ELI − : negative elastic lamina invasion; ELI + : positive elastic lamina invasion; EL − : unidentified elastic lamina. a Sigmoid colon cancer; Cancer cells do not invade the EL, i.e. pT3ELI − is defined as pT3a. b Sigmoid colon cancer; Cancer cells invade beyond the EL, i.e. pT3ELI + is defined as pT3b. c Ascending colon cancer confined to the posterior wall; EL is not identified in the adipose tissue of the adventitia, i.e. pT3EL − is defined as pT3u. d Rectosigmoid colon cancer: Cancer cells are exposed to the serosal surface and peritoneal cavity, defined as pT4a