Clinically aggressive pseudomyxoma peritonei: a variant of a histologically indolent process.

Background: Three distinct morphologic types of pseudomyxoma peritonei syndrome have been defined: disseminated peritoneal adenomucinosis (DPAM), peritoneal mucinous carcinoma (PMCA), and a hybrid morphologic type. Prognosis is best in patients with DPAM; unfortunately, some patients with DPAM succumb to a rapidly progressive disease process.

Methods: We identified a subset of 11 patients with a histopathology of DPAM but a clinical course showing an invasive disease process. As a comparison group, from a database of 501 patients with pseudomyxoma peritonei, we selected 22 age- and sex-matched controls with a DPAM histology who are alive with no evidence of disease. Clinical factors were identified for comparison of case and control groups. Expression of mucin antigens, mucin (MUC)1 and MUC2, were evaluated using immunohistochemistry.

Results: The study group consisted of 11 patients (five men and six women), with a median survival of 52.2 months (SD 7.46) and a 31% 5-year survival. All 22 matched control cases (10 men and 12 women) are alive and disease-free. Clinical data on the study and control groups including co-morbidity were similar. No significant difference in the expression of MUC1 (P = 0.74, Fisher's exact test) or MUC2 (P = 0.34, Fisher's exact test) was demonstrated between groups.

Conclusions: Further investigation of pseudomyxoma peritonei at a molecular and genetic level may help to formulate a more comprehensive classification.