Specifically: pTis indicates tumor confined to the appendiceal wall, with mucin or epithelial lesions present within the muscularis but without penetration—this stage carries a favorable prognosis; pT3 denotes extension through the muscularis into the subserosa or mesoappendix without involvement of the serosal surface; pT4a denotes mucin or epithelial cells reaching the visceral peritoneum, a finding that requires differentiation from intraoperative contamination or reactive tissue changes; and pT4b denotes direct invasion of or adhesion to adjacent organs. The gene discussed is MUC5AC; the disease is neoplasm.