Immunodetection of neuron-specific enolase and keratin in cytological preparations as an aid in the differential diagnosis of lung cancer

The results of neuron-specific enolase (NSE) and keratin immunodetection in cytological specimens of sputum secured from 41 patients with lung cancer are presented. All 19 cases of small-cell carcinoma showed intense immunoreactivity for NSE. No such immunoreactivity was found in 21 of 22 cases of non-small-cell carcinoma. The single positive result was from a case of large-cell undifferentiated carcinoma. All 10 cases of squamous-cell carcinoma showed immunoreactivity for keratin. The 19 cases of small-cell carcinoma showed no such reactivity. Our findings indicate that immunostaining for NSE and keratin is a valuable aid when a definite diagnosis of small-cell carcinoma of the lung can not be made on the basis of conventional cytologic features.