Cecilia Ceribelli,M. Gomes David,A. Ayav,J. Raft,A. Leroux,F. Marchal, Unusual Case of Pseudomyxoma Peritonei of a Mature Teratoma in Adult Men Case Reports and Series in Surgery 2020 2733-2241 http://dx.doi.org/10.31487/j.CRSS.2020.02.04 https://www.sciencerepository.org/unusual-case-of-pseudomyxoma-peritonei-of-a-mature-teratoma-in-adult_CRSS-2020-2-104 Abstract: Pseudomyxoma peritonei (PMP) is a rare disease usually originating from appendiceal neoplasm and its incidence is 1-2 cases per million. Extra-appendicular origin is less common and is related to ovary, urachus, stomach, colon and pancreas cancer. A few cases of mature ovarian teratoma associated with PMP have been described. We report an extremely rare case of a man treated for a mature teratoma recurrence as a PMP. A 57-year-old man with multiple surgeries for mature teratoma excision as a newborn was addressed to our institution. At the age of 55, a surgical exploration found a low-grade PMP. The patient was asymptomatic, and surveillance was performed. Nine months later, a sub-complete cytoreductive surgery (CRS) with Mitomycin C HIPEC (hyperthermic intraperitoneal chemotherapy) was performed. One year later, the residual mass volume was treated by a new CRS with Mitomycin C HIPEC. After a two-year follow-up patient has no recurrence. PMP extra-appendiceal origin in less than 10%. This is the first reported case of PMP originating as a mature teratoma recurrence in a man. A few cases describe PMP from ovarian teratoma in women. Despite PMP’s different origins, gold standard treatment still remains CRS and HIPEC.Keywords: Teratoma, pseudomyxoma, HIPEC