Diffuse mesothelioma of the peritoneum: correlation between histological and clinical parameters and survival in 73 patients

Summary There are few studies addressing survival of diffuse peritoneal mesotheliomas (DPM). In this study, survival data were obtained retrospectively from 73 patients treated with intended cytoreductive surgery for DPM, with a mean follow-up of 42 months. Mesotheliomas were classified as well differentiated papillary (WDPM, n = 2), multicystic (MCM, n = 4), and epithelioid mesotheliomas were subclassified as tubulopapillary (TPM, n = 27), solid/deciduoid (S/DM, n = 34), and or biphasic mesothelioma (BPM, n = 6). Invasion was characterised as absent (grade 0), into stroma (grade 1), into fat (grade 2), and into adjacent structures (grade 3). Peritoneal cancer index (PCI) and completeness of cytoreduction (CCR) were assessed surgically. There were no deaths in the WDPM, MCM, and epithelioid DPM with ⩽ grade 1 invasion. There was a stepwise decrease in overall survival from invasive TPM, S/DM, and BPM (p < 0.0001). By univariate analysis, advanced age (p = 0.01), incomplete CCR (p < 0.001), PCI (p = 0.004), mitotic count (p < 0.001), nuclear grade (p < 0.0001), stromal inflammation (p = 0.013), depth of invasion (p < 0.0001), necrosis (p = 0.002), and sarcomatoid growth (p < 0.0001) were associated with decreased overall survival. By multivariate analysis, only sarcomatoid growth (p = 0.0006), depth of invasion (p = 0.02), elevated CCR (CCR 2–3) (p = 0.02), and presence of inflammatory stroma (p = 0.04) were significant variables associated with decreased overall survival. DPM form a spectrum of indolent to highly aggressive tumours. Solid epithelioid/deciduoid tumours have a prognosis intermediate between biphasic mesotheliomas and invasive TPM. The presence and degree of invasion, sarcomatoid features, and inflammatory stroma are poor prognostic indicators.