Primary Epithelial Malignancies

Lung cancer is the most common cancer in the world and is the leading cause of cancer deaths in both men and women in the United States. Almost all primary malignant neoplasms of lung (99.0%) are carcinomas. Four types: squamous cell carcinoma, adenocarcinoma, small cell carcinoma, and large cell carcinoma, constitute the majority of tumors. Carcinoid tumors, typical and atypical, comprise a small proportion of lung neoplasms. They belong to the category of neuroendocrine neoplasms which include large cell neuroendocrine carcinoma and small cell carcinoma; but they differ from the latter in regard to association with smoking, prognosis, and some other clinical aspects. Some lung carcinomas may have neuroendocrine differentiation demonstrated by immunohistochemistry without the characteristic microscopic features of neuroendocrine differentiation. Although this could occur in all non-small cell carcinomas, it is most commonly seen in adenocarcinomas. These tumors are reported according to their histological type with a note indicating the neuroendocrine differentiation.