DISSEMINATED PERITONEAL ADENOMUCINOSIS AND PERITONEAL MUCINOUS CARCINOMATOSIS - A CLINICOPATHOLOGICAL ANALYSIS OF 109 CASES WITH EMPHASIS ON DISTINGUISHING PATHOLOGICAL FEATURES, SITE OF ORIGIN, PROGNOSIS, ANDRELATIONSHIP TO PSEUDOMYXOMA-PERITONEI

Pseudomyxoma peritonei (PMP) is a poorly understood condition characte rized by mucinous ascites and mucinous implants diffusely involving th e peritoneal surfaces. There is considerable debate regarding the defi nition, pathology, site of origin, and prognosis of PMP. We analyzed t he clinicopathologic features of 109 cases of multifocal peritoneal mu cinous tumors to develop a pathologic definition of cases characterize d by the clinical condition PMP. Cases were separated into two diagnos tic categories: disseminated peritoneal adenomucinosis (DPAM) and peri toneal mucinous carcinomatosis (PMCA). Cases classified as DPAM were c haracterized by peritoneal lesions composed of abundant extracellular mucin containing scant simple to focally proliferative mucinous epithe lium with little cytologic atypia or mitotic activity, with or without an associated appendiceal mucinous adenoma. Cases classified as PMCA were characterized by peritoneal lesions composed of more abundant muc inous epithelium with the architectural and cytologic features of carc inoma, with or without an associated primary mucinous adenocarcinoma. Sixty-five of the 109 cases (59.6%) were classified as DPAM consistent with origin from an appendiceal mucinous adenoma. Thirty-seven of the 65 cases (56.9%) had a documented appendiceal mucinous adenoma. Thirt y cases (27.5%) were classified as PMCA consistent with origin from an appendiceal or intestinal mucinous adenocarcinoma. Fourteen cases (12 .8%) were classified as PMCA with features intermediate between DPAM a nd PMCA or with discordant features based on the finding of at least f ocal areas of carcinoma in the peritoneal lesions, whether or not the primary site demonstrated carcinoma. The cases with intermediate featu res were derived from well-differentiated appendiceal or intestinal mu cinous adenocarcinomas and had peritoneal lesions displaying features of DPAM as well as focal areas of mucinous carcinoma. The cases with d iscordant features were derived from atypical appendiceal adenomas wit h little or no histologic evidence of a transition from adenoma to car cinoma and had peritoneal lesions uniformly composed of mucinous carci noma. There was a statistically significant difference in survival bet ween cases classified as DPAM, those classified as PMCA with intermedi ate or discordant features, and those classified as PMCA (p < 0.0001). The age-adjusted 5-year survival rates were 84% for patients with DPA M, 37.6% for patients with PMCA with intermediate or discordant featur es, and 6.7% for patients with PMCA. The term DPAM should be used to d iagnose the histologically benign peritoneal lesions associated with r uptured appendiceal mucinous adenomas and those that are pathologicall y identical but lack a demonstrable appendiceal adenoma. Cases with th e pathologic features of adenocarcinoma should be designated PMCA beca use they have recognizably different pathologic features and a signifi cantly worse prognosis.