: The present study aims the prognostic significance of the histologic classification of peritoneal disease of pseudomyxoma peritonei(PMP)from appendix.

Methods: During the last 15 years, 1,117 patients were histologically diagnosed for primary and peritoneal disease components according to the new WHO classification by Carr. Primary appendiceal tumors are classified into low grade appendiceal mucinous neoplasm(LAMN), high grade appendiceal mucinous neoplasm(HAMN), and mucinous neoplasm with signet ring cell carcinoma(Sig). The histologic types of peritoneal disease components were classified into four groups, ie, acellular mucin(AM), mucinous carcinoma peritonei with low grade histologic feature(LGMCP), that with high grade histologic type(HGMCP), high grade mucinous carcinoma peritonei with signet ring cells(HGMCP-S).

Results: Among 1,117 primary tumors, 834(74.7%), 221(19.8%), and 62(5.5%)shows LAMN, HAMN and Sig, respectively. Histologic types of peritoneal disease from LAMN changed to AM, HGMCP, and HGMCP-S. were found in 251 (30.1%), 173(20.7%), and 19(2.3%), respectively. Among 221 patients with HAMN, histologic type of peritoneal disease changed to AM, LGMCP, and HGMCP-S in 12(5.4%), 15(6.8%)and 35(15.8%), respectively, Among 62 patients whose primary tumors were Sig, 4(6.5%), 5(8.1%), and 5(8.1%)showed AM, LGMCP, and HGMCP, respectively. Patients with AM shows the best survival curves with 10 year-survival rate of 86.9%. The 10-year survival rates of LGMCP, HGMCP, and HGMCP-S were 63.7%, 32.2%, and 10.1%, respectively(p=0.00023). In patients with primary tumor showing LAMN, the 10-year survival rates of AM, LGMCP, HGMCP, and HGMCP-S of peritoneal disease were 91.9%, 73.2%, 49.6%, and 23.9%, respectively(p<0.0001). In patients with primary tumor showing HAMN without signet ring cell component, the 10-year survival rates of AM or LGMCP and HGMCP or HGMCP-S were 58.6%, and 21.6%, respectively(p<0.001). In patients with primary tumor having signet ring cell component, 10-year survival rates of AM or LGMCP and HGMCP or HGMCP-S were 61.3% and 19.4%, respectively.

Conclusions: Postoperative survival of patients with PMP significantly correlates with pathologic features of peritoneal disease. Accordingly, CRS should be performed after the intraoperative pathologic diagnosis of peritoneal disease.