The key step in progression from LAMN to PMP is the extravasation of mucin from the appendix into the peritoneum and this can exhibit a cellular component spreading along the peritoneum, or be acellular with mucinous ascites (LAMN 1 (pTis, pT3+) – no perforation; LAMN 2 (pT4a+) – perforated mucin into the peritoneal cavity). Here, MUC5AC is linked to pseudomyxoma peritonei.