Background: Cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS/HIPEC) has dramatically improved the survival of patients with epithelioid peritoneal mesothelioma. It is unknown if CRS/HIPEC is indicated for the more aggressive biphasic mesothelioma variant.Methods: A retrospective analysis of the Peritoneal Surface Oncology Group International (PSOGI) registry including data from 33 centers was performed. Survival was reviewed based on mesothelioma type, completion of cytoreduction, and volume of disease. Results: Overall, 484 of 1165 (41.5%) CRS/HIPEC procedures with complete CC0 and CC1 cytoreductions were analyzed; 450 (93%) procedures were performed for epithelioid mesotheliomas, while 34 (7%) were performed for biphasic mesotheliomas. For patients with CC0 resection, 5-year survival was 64.5 and 50.2% (median 7.8 and 6.8 years; p = 0.015) for epithelioid and biphasic mesotheliomas, respectively, while inclusion of CC1 resections in the analysis resulted in inferior 5-year survival of 62.9% and 41.6% (median 7.8 and 2.8 years; p = 0.0012), respectively. Incomplete CC2 resections for biphasic primaries resulted in a median survival of 4.3 months. Univariate analysis of the biphasic cohort indicated Peritoneal Cancer Index (PCI; p = 0.015), CC status of resection (p < 0.0001), and Ki67 (p = 0.04) as predictors of survival. Systemic chemotherapy before (p = 0.55) or after (p = 0.7) CRS/HIPEC did not influence survival. In multivariate analysis, only PCI (p = 0.03) and CC (p = 0.04) remained significant. Conclusions: Long-term survival is achievable in patients with low-volume biphasic mesothelioma after complete macroscopic cytoreduction. Biphasic peritoneal mesotheliomas should not be considered as an absolute contraindication for CRS/HIPEC if there is low-volume disease and if complete cytoreduction can be achieved.
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