Knowledge of pulmonary neuroendocrine tumors: where are we now?

ranging from the low-grade typical carcinoid(TC), to highly aggressive, poorly differentiatedtumors (large-cell neuroendocrine carcinoma,LCNC, and small-cell lung cancer, SCLC). Amidthem, an intermediate-grade neoplasm (atypicalcarcinoid, AC) is characterized by a greateraggressive biological behavior, compared to TCwith a poorer 5-year survival and a higher ten-dency to lymph-nodal involvement at presenta-tion. TCs and ACs are categorized together ascarcinoids; LCNC is considered a subgroup oflarge-cell carcinomas, and SCLC is an indepen-dent class of lung cancer.NETs derive from the pulmonary neuroendo-crine cells (PNECs), which are of endodermalorigin, regardless of their phenotypic resem-blance to neurons.