Re-Evaluation of Diagnosis of ‘Benign’ Colon Polyp

Purpose: In about 80% of cases, colon cancer develops from alterations of the APC (adenoma-carcinoma sequence) pathway. An ‘alternative pathway’ involving variants of hyperplastic polyps (serrated polyps), MSI and BRAF mutation may account for 20%. The ‘serrated polyp classification’ divides polyps into various histological subtypes. Emerging evidence suggest that certain subtypes may have neoplastic potential. Our purpose was to re-evaluate the histological diagnosis in patients previously diagnosed as ‘hyperplastic polyp’ and ‘adenoma’. Methods: We randomly selected histology slides of 45 pts with the diagnosis of ‘Hyperplastic polyp’ and 49 pts with the diagnosis of ‘Adenoma’ at the John Dempsey hospital (year 2002–03). All slides were re-classified based on following new classification. 1) Hyperplastic polyp a) Microvesicular serrated polyp (MVSP) b) Goblet cell serrated polyp (GCSP) c) Mucin poor serrated polyp (MPSP) 2) Sessile serrated adenoma (SSA) 3) Traditional serrated adenoma/serrated adenoma (TSA) 4) Conventional adenoma (tubular, villous, TV) Results: ‘Hyperplastic polyp’ were reclassified with the GCSP (least deviated from classic hyperplastic definition) to those TSA which have some adenomatous change (Table). Importantly, a high 61% were MVSP which may harbor BRAF mutation and have, as a class, malignant potential.Table: Hyperplastic group.Conclusion: Using histologic criteria for serrated polyps, 91% lesions (combining MVSP and TSA) are currently recognized as lesions with possible malignant potential. Historically, patients with ‘hyperplastic’ polyps were not recommended for increased colon surveillance but ‘reclassification’ of previous histologic diagnosis may warrant shorter follow up intervals. Larger prospective clinical trials are needed to ascertain the prognosis and outcome of described histology.Table: Adenoma group.Figure: Microvesicular serrated polyp (MVSP).Figure: Traditional serrated adenoma (TSA).