Approach to the diagnosis of neuroendocrine lung neoplasms: variabilities and pitfalls.

With the publication of the spectrum of neuroendocrine proliferations and neoplasms and the features and criteria for diagnosing neuroendocrine lung neoplasms, there is more agreement in making a specific pathologic diagnosis of a neuroendocrine lung neoplasm. However, problems exist, especially in diagnosing well-differentiated neuroendocrine carcinomas (atypical carcinoids), large-cell neuroendocrine carcinomas, and even some small-cell lung cancers. Some of this disagreement has to do with a pathologist's perception of sizes and shapes of cells. Nonneuroendocrine small-cell carcinomas exist and include small-cell squamous cell carcinoma, small cell adenocarcinoma, and basaloid carcinoma. Nonneuroendocrine lung cancers, especially large-cell undifferentiated carcinoma and poorly differentiated adenocarcinoma, not infrequently express neuroendocrine markers immunohistochemically.