A novel tumor-node-metastasis (TNM) staging system of diffuse malignant peritoneal mesothelioma using outcome analysis of a multi-institutional database*.

BACKGROUND: Currently, no tumor-node-metastasis (TNM) staging system exists for patients with diffuse malignant peritoneal mesothelioma (DMPM). The primary objective was to formulate a clinicopathological staging system through the identification of significant prognostic parameters.
METHODS: Eight international institutions with prospectively collected data on patients who underwent cytoreductive surgery and hyperthermic intraperitoneal chemotherapy contributed to the registry. Two hundred ninety-four patients had complete clinicopathological data and formed the basis of this staging project.
RESULTS: Peritoneal cancer index (PCI) was categorized into T(1) (PCI 1-10), T(2) (PCI 11-20), T(3) (PCI 21-30), and T(4) (PCI 30-39). Twenty-two patients had positive lymph nodes (N(1) ) and 12 patients had extra-abdominal metastases (M(1) ). The survival for patients with T(1) (PCI 1-10) N(0) M(0) was significantly superior to the other patients. This group of patients is therefore designated as Stage I. The survival of patients with T(2) (PCI 11-20) and T(3) (PCI 21-30), in absence of N(1) or M(1) disease, was similar. This group of patients was categorized as Stage II. The survival of patients with T(4) (PCI 30-39), N(1,) and/or M(1) was similarly poor. This group of patients was therefore categorized as Stage III. Three prognostic factors were independently associated with survival in the multivariate analysis: histological subtype, completeness of cytoreduction, and the proposed TNM staging. The 5-year survival associated with Stage I, II, and III disease was 87%, 53%, and 29%, respectively.
CONCLUSIONS: The proposed TNM staging system resulted in significant stratification of survival by stage when applied to the current multi-institutional registry data.