Neuron-specific enolase in neuroendocrine tumors of the thymus, bronchus, and skin.

In order to better define the use of neuron-specific enolase (NSE) as a marker for neuroendocrine neoplasms, we studied 11 thymic carcinoid tumors, three bronchial small-cell carcinomas (all with cutaneous metastases), and 10 trabecular carcinomas of the skin for its presence, using the peroxidase-antiperoxidase (PAP) technic with an antiserum directed at NSE. All 11 carcinoid tumors stained positively, as did two of the bronchial small-cell carcinomas and seven of the trabecular carcinomas. We conclude that PAP staining for NSE content may be a useful adjunct to morphologic analysis in diagnostically identifying the tumors we studied and that our results support the concept of a functionally unified APUD system, as reflected in the tumors originating from it. Nevertheless, because of the vagaries of the PAP method, exemplified by the results in our small series, it cannot be relied upon as a sole indicator that a tumor contains NSE and is therefore neuroendocrine. Also, since it is hypothesized that NSE is present in all tumors of this type, staining for its presence would seem to be of little benefit in distinguishing primary from secondary neuroendocrine tumors or in identifying the origin of metastatic lesions that have a neuroendocrine histologic appearance.