CEA and CA 19‐9 in benign pulmonary or mediastinal cystic lesions

Serum carbohydrate antigen (CA) 19-9 was present at high levels in pulmonary sequestration, mediastinal bronchogenic cysts, and mediastinal mature teratomas. The fluid in the cysts of the lesions contained a high level of CA 19-9. After operation, the titer of serum CA 19-9 returned to normal ranges. Histological studies showed that mucosal epithelium stained positively for CA 19-9. We speculate that CA 19-9 concentrated in the cystic lesion might flow into the peripheral blood. Carcinoembryonic antigen (CEA) was also present at high levels in the cyst fluid. CEA was positively stained in the epithelial cells using a polyclonal antibody but not a monoclonal antibody. The CEA detected at high concentration in the fluid was considered to be immunologically cross-reacting CEA.