High reproducibility is attainable in assessing histoprognostic parameters of pT1 colorectal cancer using routine histopathology slides and immunohistochemistry analyses.

Assessment of the risk of lymph node invasion and tumour recurrence is critical to determine whether additional surgery is required in patients with endoscopically-removed pT1 colorectal cancer (CRC). A reproducible assessment of this risk of recurrence based on histopathological parameters is crucial for relevant therapeutic decisions. The inter-observer reproducibility of these parameters was the subject of our study. Two pathologists independently analysed 163 endoscopically-removed pT1 CRC recorded in a local digestive cancer registry database (Finistère, France). Using haematoxylin-eosin-saffron (HES) and immunohistochemistry slides, they evaluated several parameters related to the risk of tumour recurrence according to the international pT1 CRC-dedicated guidelines. Based on Kappa and intra-class correlation coefficients, good to very good inter-observer agreement was obtained by analysing vertical and lateral margins, submucosal invasion, tumour differentiation and lymphovascular invasion. The reproducibility of tumour budding quantification was only fair on the basis of HES slides but reached a very good agreement using cytokeratin immunohistochemistry. Dual colour cytokeratin and podoplanin immunohistochemistry also improved inter-observer agreement for the detection of lymphovascular invasion. All patients with loco-regional nodal metastases (7 of 101 who underwent complementary surgery) or distant metastases (3 patients) were diagnosed as having a high risk of recurrence and requiring an additional surgery by the two observers. Our study showed that good to very good inter-observer agreement is achievable in evaluating the pathological parameters of recurrence risk in endoscopically-removed pT1 CRC. In addition to HES slides, the detection of lymphovascular invasion and tumour budding can benefit with more reproducible immunohistochemical analyses.