Rapamycin treatment for benign multicystic peritoneal mesothelioma: A rare disease with a difficult management

Objective: Unusual or unexpected effect of treatment Background: Benign multicystic peritoneal mesothelioma (BMPM) is a rare intra-abdominal tumor. Although considered by many to be benign, this tumor has a high local recurrence rate. Because of its rarity, preoperative diagnosis is difficult and its origin and pathogenesis are uncertain. There are no evidence-based treatment strategies for BMPM. It is agreed that the best treatment strategy for BMPM is the combination of surgical cytoreduction and hyperthermic intraperitoneal chemotherapy (HIPEC). An increasing body of evidence supports a pivotal role of the cytoplasmic serine/threonine kinase mTOR in the development and progression of several neoplastic diseases and specific mTOR inhibitors, including rapamycin, have been suggested as potential therapeutic options for different cancers. Case Report: A 65-year-old male with end-stage renal disease on hemodialysis for seven years presented with BMPM. He underwent surgery to remove multiple peritoneal cysts, but four months later he experienced a recurrence of the disease. Immunohistochemistry of the cysts demonstrated a high level of phosphorylation of p70S6 kinase, a downstream mTOR target, and since a target therapy that blocks PI3K/Akt/mTOR pathway has been shown to have a scientific and logical rationale to treat this rare intra-abdominal neoplasia, we started the patient on low dose rapamycin therapy, an mTOR inhibitor. Long-term mTOR inhibition resulted in a complete and stable remission of BMPM. Conclusions: The current case is the first report of BMPM successfully treated with rapamycin, which resulted in a long-last-ing response to mTOR inhibition.