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. Diagn Cytopathol 1986;2:217‐220.