The diagnosis of primary lung cancer with special reference to sputum cytology

Of 2,545 in-patients with primary lung cancer, pathological proof of the diagnosis was obtained by sputum cytology in 48%, by bronchoscopy in 32%, by biopsy from miscellaneous sites in 12%, and at thoracotomy or necropsy only in 19%. The diagnosis was made solely on clinical and radiological evidence in 8%. One or more satisfactory specimens of sputum from 2,035 patients gave a positivity rate of 59%. When three specimens of sputum were tested the positivity rate was 69% and when four or more were tested, 85%. The maximum false positivity rate was 0·7%. Agreement between the types of malignant cells found in the sputum and in resected or necropsy specimens occurred in 84%. The pathological diagnosis was based solely on sputum cytology in 40% of the patients in whom malignant cells were found in the sputum. The total work of the sputum laboratories was analysed for one year (1967); sputum was examined from 1,598 patients, of whom 266 (17%) had positive results. Of 1,518 patients who had a bronchoscopy, the positivity rate was 53%, and of 524 patients with biopsies from miscellaneous sites the rate was 64%. Sputum cytology, as practised at present, is a very valuable method of diagnosis, but its demands on time and expertise make it unsuitable for general application outside large medical centres.