Connecting the dots: Low-grade appendiceal mucinous neoplasms and serrated polyps in the appendix.

Objective: This study aimed to examine the relationship between low-grade appendiceal mucinous neoplasms (LAMNs) and serrated polyps (SPs) of the appendix, both characterized by KRAS mutations and overlapping morphologic features.

Methods: We analyzed 27 cases of LAMN and 24 cases of SP from archival records, reviewed pathology, and performed molecular analysis on select cases. Four cases initially diagnosed as LAMN were excluded for not meeting diagnostic criteria, and 1 SP case was reclassified as LAMN.

Results: Microscopic evaluation revealed serrated architecture in 8 (29.6%) of 27 LAMNs: 4 hyperplastic polyp-like, 2 sessile serrated lesion-like (SSL), and 1 traditional serrated adenoma-like (TSA). One case exhibited both SSL- and TSA-like areas. Among SPs, 3 (12.5%) of 24 cases showed morphologic overlap with LAMN due to cytoplasmic mucin, flattened mucosa, and conventional adenoma-like features; all were grossly visible. KRAS was the most common mutation in LAMNs with serrated architecture (4/4, 100%), 1 classic LAMN, and 1 SP with dysplasia and associated signet-ring cell carcinoma.

Conclusions: Serrated polyps and LAMNs likely represent a biological continuum, sharing key features such as KRAS mutations and morphologic overlap. Our findings underscore the need for careful molecular and histopathologic evaluation in diagnosing these neoplasms.