ROS1-positive lung adenocarcinoma presenting with cancer spread across the abdomen

What happened, in summary

A 56-year-old man who had never smoked was admitted after a month of fever, night sweats, shortness of breath, cough, nausea, diarrhea, abdominal pain, and increasing abdominal swelling. Antibiotics for presumed pneumonia had produced little improvement. Initial assessment also considered liver disease because of the ascites.

CT of the abdomen showed extensive nodularity across the omentum, consistent with peritoneal carcinomatosis. No obvious primary lung tumor was visible on chest imaging. Omental biopsy and analysis of pleural and peritoneal fluid nevertheless confirmed metastatic lung adenocarcinoma. A second pathology review at a specialist cancer center supported the diagnosis.

Molecular testing found a ROS1 rearrangement, and the case also described high PD-L1 expression. He began crizotinib 250 mg twice daily. His cough, shortness of breath, abdominal pain, distention, and leg swelling improved. Mild nausea and diarrhea continued.

After two months, CT showed markedly smaller pleural effusions, resolution of the ascites and peritoneal thickening, and major improvement in the extensive omental disease. At six months, imaging showed no residual disease, and he remained on crizotinib without evidence of progression. His course shows how molecular testing identified a treatment option even when the lung primary was not visible and the cancer first appeared through abdominal and pleural spread.