Systemic metastases from low-grade and high-grade pseudomyxoma peritonei: Treatments and outcomes

The metastasizing potential of pseudomyxoma peritonei (PMP) is largely unknown. We assessed incidence, impact on prognosis, treatments, and outcomes of systemic metastases after cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS/HIPEC).

A prospective database of 327 patients undergoing CRS/HIPEC for PMP of appendiceal origin was reviewed. PMP was graded according to the Peritoneal Surface Oncology Group International (PSOGI) classification. Haematogenous metastases, and non-regional lymph-node involvement were considered as systemic metastases.

After a median follow-up of 74.8 months (95% confidence interval [CI] = 68.0-94.8), systemic metastases occurred in 21 patients. Eleven patients were affected by low-grade PMP, and ten by high-grade PMP. Metastatic disease involved the lung (n = 12), bone (n = 1), liver (n = 4), distant nodes (n = 3), both lung and distant nodes (n = 1). Systemic metastases independently correlated with PSOGI histological subtypes (P = 0.001), and incomplete cytoreduction (P = 0.026). Median OS was 139.0 months (95%CI = 56.6-161.9) for patients who experienced systemic metastases, and 213.8 months (95%CI = 148.7-not reached) for those who did not (P = 0.159). Eight of eleven patients who had curative-intent surgery are presently alive at a median of 52.5 months (range 2.0-112.7). Seven are disease-free at a median of 27.4 months (range 2.0-110.4). At multivariate analysis, PSOGI histological subtypes (P = 0.001), completeness of cytoreduction (P = 0.001), and preoperative systemic chemotherapy (P = 0.020) correlated with poorer survival. Systemic metastases did not (P = 0.861).

After CRS/HIPEC, systemic metastases occur in a small but clinically relevant number of patients, and the risk increases with incomplete cytoreduction and aggressive histology. In selected patients, surgical resection of metastatic disease can result in long survival.