RT Journal Article SR Electronic T1 Primary peritoneal mucinous cystadenocarcinoma mimicking possible recurrent ovarian mucinous cystadenoma: coincidental pathology or a spectrum of disease? JF BMJ Case Reports JO BMJ Case Reports FD BMJ Publishing Group Ltd SP e242478 DO 10.1136/bcr-2021-242478 VO 14 IS 7 A1 Claire Filippini A1 Sarah Smyth A1 Hooman Soleymani Majd A1 Catherine Johnson YR 2021 UL http://casereports.bmj.com/content/14/7/e242478.abstract AB We present the case of a 32-year-old woman with a previous surgical history of benign mucinous cystadenoma resected in 2012 who underwent magnetic resonance cholangiopancreatography following her second pregnancy in 2020. This demonstrated a large cystic mass in the left subdiaphragmatic space. Histopathology confirmed a well-differentiated primary peritoneal mucinous cystadenocarcinoma displaying cells of a Mullerian origin. We subsequently discuss the aetiology of these conditions separately and explore the possibility of a connection between the two regarding origin or potential malignant transformation that may otherwise have occurred coincidentally in this young patient. We also acknowledge a paucity of evidence regarding subsequent management strategies.