Carbohydrate antigen 19-9 (CA 19-9) is an independent prognostic indicator in pseudomyxoma peritonei post cytoreductive surgery and perioperative intraperitoneal chemotherapy.

INTRODUCTION: Pseudomyxoma peritonei (PMP) is characteristically divided into two histopathological subtypes; disseminated peritoneal adenomucinosis (DPAM) and peritoneal mucinous carcinomatosis (PMCA). The latter is associated with a worse prognosis. However, even within the DPAM group, there is a considerable variation in outcome. In this study we investigate the role of baseline serum tumor markers CA 19-9, CEA and CA-125 in further stratifying survival.

METHODS: Over 16 years, 218 patients with PMP were treated with cytoreductive surgery (CRS) and perioperative intraperitoneal chemotherapy (PIC) at our institution. A CA-125 level of >35 U/L, CA 19-9 of >40 U/mL and CEA of >3 ng/mL were considered positive or elevated outside the laboratory reference range. The impact of clinicopathologic and treatment-related variables on overall survival (OS) was analyzed with the Kaplan Meier method. Survival curves were compared using the log-rank test. Variables deemed significant by univariate analyses were entered into multivariate analysis using the Cox proportional hazards model.

RESULTS: Within the DPAM group, the 5-year survival of patients who were CA 19-9 positive versus those with normal values were 58% and 90% respectively (P<0.001). Other variables found to negatively impact on OS in univariate analyses were completeness of cytoreduction (CC) score 2/3 (P<0.001), peritoneal cancer index (PCI) >25 (P<0.001) and male gender (P=0.017). In the Cox regression model, only CA 19-9 positivity was found to be an independent prognostic factor for OS (P=0.034). In addition to marker positivity, the absolute level of CA 19-9 was also prognostically significant. In patients with CA 19-9>1,000 U/mL, the 5-year survival was 23%, in contrast to 90% in patients with CA 19-9<100 U/mL (P<0.001). In the PMCA cohort, only CC-score was found to be associated with OS (P<0.001).

CONCLUSIONS: Our study provides relevant prognostic information for the DPAM subtype in staging and prioritizing surgery; as even in apparently indolent disease, some patients have poorer survival. CA 19-9 elevation may also be useful in identifying patients who would potentially benefit from adjuvant therapy and/or closer post-operative surveillance. The potential role of CA 19-9 in mediating tumor cell adhesion and disease progression in PMP should be further investigated to deepen our understanding of the disease's inherent biological behavior. If a true relationship exists, CA 19-9 may be a conceivable target for immunotherapy.