ROS1-rearranged lung adenocarcinoma with peritoneal carcinomatosis on initial presentation.

Peritoneal carcinomatosis (PC) is progression of the primary cancer to the peritoneum that is seen in only 1.2% of patients with lung cancer. It is associated with poor prognosis especially if present at the time of initial cancer diagnosis. The predisposing factors for peritoneal spread are not yet well understood. It has been suggested that the oncogene status of the tumour can influence the patterns of metastatic spread. There is not enough data about the role of c-ROS oncogene 1 (ROS1) mutation in the development of PC in non-small cell lung cancer. Here, we describe a case of a 56-year-old man who presented with new-onset ascites and was found to have PC. He was diagnosed with ROS1-rearranged lung adenocarcinoma. No obvious primary tumour was identified. Patient responded well to targeted therapy with crizotinib and remained 6 months free of disease progression. © BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.