Clinicopathologic characteristics and histogenesis of mucinous tumor of peritoneum

Objective To investigate the clinicopathologic characteristics, prognosis and histologic origin of the mucinous tumor of the peritoneum. Methods According to 2010 WHO classification of tumours of the digestive system, 34 cases diagnosed as "pseudomyxoma peritonei ( PMP) " were reevaluated and divided into low grade and high grade. Immunohistochemistry was applied to investigate the expression of SATB2 and the histologic origin of the mucinous tumor of the peritoneum, using antibodies against SATB2, CK7, CK20 and CDX-2. The relationship between clinicopathologic characteristics and prognosis of the low grade and high grade tumors were analyzed. Results Twenty five patients had low grade mucinous tumors ( two of them were no cell type ), nine patients had high grade mucinous tumors. There was no significant difference between low grade and high grade mucinous tumors in age, sex, recurrence and organs involvement (P > 0.05). Thirty patients were followed up, the overall survival rates of patients with low grade and high grade mucinous tumors were 13/21 (61.9%) and 3/9, respectively. The median survival time was 74 and 24 months in low and high grade patients, and the difference was statistically significant (P = 0. 002). Immunohistochemistry showed the expression rates of CDX-2, CK20, and CK7 in totally 32 cases (excluding 2 cases of no cell type) were 30/32 (93.8%), 31/32 (96.9%), and 3/16, respectively; the expression rates of CDX-2, CK20, and CK7 in 16 cases with distinct primary site were 15, 16, and 1 , respectively ; fifteen of 16 cases of tumors of unknown primary site were positive for CDX-2 and CK20, two of the them were positive for CK7. There was no difference in the expression of CDX-2, CK20 and CK7 between tumors with distinct primary site and tumors with unknown primary site ( P > 0. 05 ). The expression rate of SATB2 in the cases was 56. 3% ( 18/32), excluding 2 cases of no cell type. There was no significant difference between low grade and high grade tumors in the expression of SATB2 [ 15/23(65. 2% ) vs 3/9, P =0. 102] , also SATB2 was not related to the prognosis of the tumor ( P = 0. 786 ). Conclusion The prognosis of the mucinous tumor of the peritoneum was significantly different between low grade and high grade according to WHO 2010 classification, and most mucinous tumor of the peritoneum originated from the appendix.