Factors affecting the rate of positivity of sputum cytology in lung cancer.

We studied the role of sputum cytology and factors influencing the rate of positivity of sputum cytology in 103 patients with lung cancer. Sputum cytology was positive in 71.8% of these patients. Of 647 specimens submitted for sputum cytology, 610 were evaluable and the positivity rate was 43.6%. Forty-eight patients had at least six sputum cytology examinations. The rate of positivity for each of these examinations was between 31.3% and 50.0%, and the cumulative rate of positivity in these 48 patients was 77.1% at the sixth examination. Factors influencing the positivity rate were the histology of the tumor, tumor size, the site of the tumor, admixture with blood and the degree of surface necrosis of the tumor. The histology suspected from the sputum cytology coincided well with that determined at the operation or necropsy in adenocarcinoma, squamous cell carcinoma and small cell carcinoma, but not in large cell carcinoma.