Controversies in the pathological assessment of colorectal cancer

Abstract

Pathologic assessment of colorectal cancer specimens plays an essential role in patient management, informing prognosis and contributing to therapeutic decision making. The tumor-node-metastasis (TNM) staging system is a key component of the colorectal cancer pathology report and provides important prognostic information. However there is significant variation in outcome of patients within the same tumor stage. Many other histological features such as tumor budding, vascular invasion, perineural invasion, tumor grade and rectal tumor regression grade that may be of prognostic value are not part of TNM staging. Assessment of extramural tumor deposits and peritoneal involvement contributes to TNM staging but there are some difficulties with the definition of both of these features. Controversies in colorectal cancer pathology reporting include the subjective nature of some of the elements assessed, poor reporting rates and reproducibility and the need for standardized examination protocols and reporting. Molecular pathology is becoming increasingly important in prognostication and prediction of response to targeted therapies but accurate morphology still has a key role to play in colorectal cancer pathology reporting.

Keywords: Colorectal cancer; Histopathology; Prognosis; Staging; Tumor-node-metastasis.

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.