[Pulmonary neuroendocrine tumors. The spectrum of histologic subtypes and current concept on diagnosis and treatment].

Neuroendocrine tumors of the lung represent a broad spectrum of morphologic types that share specific morphologic, immunohistochemical, ultrastructural, and molecular characteristics. The classification of neuroendocrine lung tumors has changed over the last decades and currently four categories are distinguished: typical carcinoid tumor, atypical carcinoid tumor, large cell neuroendocrine carcinoma and small cell carcinoma. Neuroendocrine tumors of the lung comprise approximately 20% of all primary lung cancers. Among them, the most frequent is small cell carcinoma (13-17%). Because of differences in clinical behavior, therapy, and prognosis, a reliable histological diagnosis, as well as clinical and pathological staging system are essential for an appropriate medical proceedings. The most effective treatment of bronchial carcinoids and large cell neuroendocrine carcinoma in an early stage is complete surgical resection, whereas chemotherapy remains the primary treatment for small cell carcinoma. All carcinoids are malignant tumors with the potential to metastasize. The majority of patients with pulmonary carcinoid have an excellent survival, even if they present with lymph node metastases. Large cell neuroendocrine and small cell carcinoma progress rapidly and are generally widespread at the moment of diagnosis. Their overall prognosis is poor. Increased knowledge about pulmonary neuroendocrine tumors biology and the genetic characteristics, imply that carcinoid tumors appear to have a different etiology and pathogenesis than large cell neuroendocrine and small cell carcinoma. In practice, it could be easiest to conceptualize this group of pulmonary tumors as a spectrum of malignancy ranging from the low grade typical carcinoid to the highly malignant large cell neuroendocrine and small cell carcinoma. Typical carcinoid tumors associated with a fairly benign behavior should be classified as low-grade neuroendocrine tumor/carcinoma (G1) and atypical carcinoid tumors as intermediate-grade tumor/carcinoma (G2). Whereas, large cell neuroendocrine and small cell carcinoma should be grouped together under the designation of high-grade neuroendocrine tumor/carcinoma (G3).