Multicystic peritoneal mesothelioma: outcomes and patho-biological features in a multi-institutional series treated by cytoreductive surgery and Hyperthermic Intraperitoneal Chemotherapy (HIPEC).

AIM: This retrospective multi-institutional study addresses the role of surgical cytoreduction and hyperthermic intraperitoneal chemotherapy (HIPEC) in the treatment of multicystic peritoneal mesothelioma (MCPM). MCPM is an uncommon tumour with uncertain malignant potential and no current standard therapy. Additionally, poorly defined pathological and biological features of this disease were investigated.

METHODS: Twelve patients with MCPM underwent 14 procedures of cytoreduction and HIPEC in two Italian referral centres. Nine patients had recurrent disease after previous debulking (one operation in six patients, two in two, four in one). Biological markers related to mesothelioma origin and clinical features were assessed by immunohistochemical studies.

RESULTS: Median follow-up was 64 months (range 5-148). Optimal cytoreduction (residual tumour nodules ≤2.5 mm) was performed in all the procedures. One grade IV postoperative complication (NCI/CTCAE v.3.0) and no operative death occurred. All the patients are presently alive with no evidence of disease, including two patients who underwent the procedure twice, due to locoregional disease recurrence. Five- and ten-year progression-free survival was 90% and 72%, accounting for a. statistically significant difference (P = 0.0001) with progression-free survival following previous debulking surgery (median 11 months; range 2-31). All cases showed low proliferative activity assessed by mitotic rate and Ki-67 expression.

CONCLUSIONS: MCPM is a borderline tumour with a high propensity to local-regional recurrence. Definitive tumour eradication by means of cytoreduction and HIPEC seems more effective than debulking surgery in preventing disease relapse. Low mitotic rate and poor Ki-67 expression might be related to the peculiar behaviour of MCMP.