Clinicopathologic impacts of poorly differentiated cluster-based grading system in colorectal carcinoma

Differentiation-based histologic grading of colorectal carcinoma (CRC) is widely used, but its clinical impact is limited by insufficient prognostic value, interobserver disagreement, and the difficulty of its application to CRC with specific histologic types such as mucinous and medullary carcinoma. A recently proposed novel grading system based on quantifying poorly differentiated clusters (PDCs) claims to have the advantages of reproducibility and improved prognostic value, and might apply to heterogeneous CRC. We aimed to validate the clinicopathologic significance of the PDCs-based grading system and to determine the relationship between this grading system and microsatellite instability (MSI). Two hundred and one patients who had undergone radical surgery were reviewed. Based on the number of PDCs, 85, 58, and 58 tumors were classified as grade (G) 1 (42.3%), G2 (28.9%), and G3 (28.9%), respectively. PDCs-based grade was significantly associated with T, N, and M stages; lymphovascular invasion; conventional histologic grade; and frequent tumor budding (all P