Controversies in the pathological assessment of colorectal cancer

Figure 1 Macroscopic and microscopic features of peritoneal involvement. A: Peritoneal puckering; B: Area with peritoneal puckering correlates with the invasive edge of the tumor on sectioning; C: Adenocarcinoma in a peritoneal cleft in a pT4a case; D: Invasion through peritoneal elastic lamina highlighted with an elastic stain.

Figure 2 Histological appearances of tumor budding and vascular invasion. A: Tumor budding; B: Cytokeratin immunohistochemical stain highlights tumor buds; C: “Orphan” artery sign - an elongated tumor profile is identified adjacent to an artery with no visible accompanying vein; D: Elastic stain highlights elastic fibres in the walls of arteries and an adjacent vein filled with tumor.

Figure 3 Pathological appearances of tumor regression. A: Regressed tumor with the appearance of a mucosal scar; B: No residual tumor seen in tumor regression grading 1 (TRG1); C: Fibrosis outgrows tumor in TRG2; D: Extensive residual tumor in TRG3.