Pulmonary well-differentiated neuroendocrine tumors are classified as either typical carcinoids (TC) or atypical carcinoids (AC) based on morphology, mitotic count and the presence or absence of necrosis. They represent 1-2% of pulmonary neoplasms and approximately 25% of all neuroendocrine tumors. At diagnosis, the vast majority are sporadic, non-functioning and typical carcinoids (TC to AC ratio 8:1). They are often diagnosed at an early stage and resected radically with a good prognosis. No adjuvant therapy is recommended after radical surgery. Everolimus constitutes the only approved drug for use in the metastatic setting, whereas somatostatin analogues, cytotoxic chemotherapy and peptide receptor radionuclide therapy are also used.
Well-differentiated NETs of unknown primary site are usually approached similarly to well-differentiated NETs of the gastrointestinal tract. They behave similar to metastatic small- intestinal NET with regard to survival. Depending upon the clinical situation, appropriate management may include local therapy or systemic therapy as somatostatin analogs, PRRT or cytotoxic therapy.