Normal bronchial mucus contains high levels of cancer-associated antigens, CA125, CA19-9, and carcinoembryonic antigen.

The presence of cancer-associated antigens CA125, CA19-9, and carcinoembryonic antigen (CEA) in apparently normal respiratory system was demonstrated histochemically and immunochemically. Epithelial cells lining central airways (trachea, bronchi, and bronchioli) and respiratory glands were specifically stained by antibodies recognizing CA125, CA19-9, and CEA. Most, if not all, bronchial mucus obtained from patients without pulmonary diseases during general anesthesia contained remarkably high levels of CA125, CA19-9, and CEA ranging from 190 to 41,000 U/ml (594-4803 U/mg protein), 210 to 95,000 U/ml (294-197,917 U/mg protein), and 6 to 940 ng/ml (14-209 ng/mg protein), respectively, whereas serum antigen levels were normal in all cases examined. These results suggest that CA125, CA19-9, and CEA are synthesized and secreted by normal epithelial cells of central airways and/or respiratory glands and that these substances are not specific indicators of abnormal cellular activity.