MUC5AC and neoplasm: Risk factors associated with recurrence or progression to PMP include histologic evidence of mucin or tumor cells breaching the serosa, appendiceal wall fibrosis with mucin infiltration, separation of mucinous masses from the primary tumor, positive intraoperative or postoperative resection margins, postoperative elevation of tumor markers (CEA, CA19-9, CA-125), and AJCC M staging of M1b.