A method of diagnosing cancer with antibodies directed to non-cellular components in non-vascular, cellular secretions is disclosed. One such antibody is the monoclonal antibody Lu4B5, which was produced by immunizing mice with a purified, mucin containing fraction prepared from pooled bronchial washings from adenocarcinoma and large cell lung cancer patients.

Lu4B5 monoclonal antibody reacts with the bronchial secretions of patients with primary bronchogenic carcinoma significantly more frequently than with secretions from patients without primary lung cancer.