A Study of Significance of Poorly Differentiated Clusters in Colorectal Carcinomas: Association with Histopathological Prognostic Factors

Abstract

Introduction: Colorectal Cancer (CRC) is the third most common cancer worldwide with prevalence rate of 47 million per five years and 1.8 million new cases per year. Routinely differentiation-based histologic grading of CRC is used, but its clinical impact is limited by insufficient prognostic value, inter-observer variability and the difficulty of its application to specific CRC’s like mucinous, micropapillary, signet ring cell and medullary carcinomas. To overcome this, Poorly Differentiated Cluster (PDC) based grading have been proposed recently in 2012 by Ueno H et al., PDC is defined as a solid cancer cell nest comprising ≥5 cancer cells, lacking a gland-like structure. Aim: To compare PDC based grading with conventional World Health Organisation (WHO) grading in resected specimens of colorectal adenocarcinomas and to evaluate the relationship of PDC grading with known prognostic histopathological parameters. Materials and Methods: The present study was a descriptive study done duration of three years and two months in the Department of Pathology, JSS Medical College and Hospital, Mysuru, Karnataka, India. A total of 60 CRC cases were studied. WHO grading was done according to eighth edition, 2018 of the American Joint Committee on Cancer (AJCC) staging system. Haematoxylin and Eosin (H&E) stained slides were studied by two pathologists and looked for inter-observer variability by k statistics. Finally, both pathologists arrived at a consensus and was subjected for PDC grading and correlated with other prognostic histological markers. The comparison of data was done by Pearson’s Chi-square test and t-test. The p-values <0.05 were considered statistically significant. Fleiss-Cohen’s weighted k statistics was used for the assessment of inter-observer variability in tumour grading. Results: There was significant association between PDC grading and WHO grading with k-value of 0.852 and p-value of 0.001. The maximum cases on PDC grading were of G-II type-29 (48.3%) followed by G-III-25 (41.7%) and G-I-6 (10%). There was increase in G-II and G-III carcinomas, as mucinous adenocarcinoma and signet ring cell carcinomas were also graded with PDC which was not possible with current WHO grading system. Conclusion: Present study findings suggest that PDC grading is more reproducible and provides better prognostic stratification as it is less subjective than the conventional WHO grading.