Immunostaining of neuron-specific enolase is a valuable aid to the cytological diagnosis of neuroendocrine tumours of the lung.

The neuroendocrine marker neuron-specific enolase (NSE) has been reported to be detectable by immunohistochemistry in paraffin sections of neuroendocrine neoplasms of the lung. There is no study of immunodetection of NSE in cytological smear preparations from these tumours. We have examined 10 cases of small cell carcinoma of the lung, using cells obtained from serous fluids or bronchial biopsies, and found all but one had NSE-like immunoreactivity. No such immunoreactivity was found in 26 serous fluids and 19 biopsies from non-small-cell carcinomas. It is suggested, therefore, that immunostaining for NSE is a valuable aid to the cytological diagnosis of small cell carcinoma of the lung.