Challenges in the Diagnosis and Management of Well-Differentiated Neuroendocrine Tumors of the Lung (Typical and Atypical Carcinoid): Current Status and Future Considerations.

Neuroendocrine tumors (NET) of the lung represent approximately 25% of all primary lung tumors and can be classified as low grade (typical carcinoids), intermediate grade (atypical carcinoids), or high grade (large cell neuroendocrine carcinoma or small cell lung carcinoma). Low- and intermediate-grade lung NET are increasingly recognized as biologically distinct from high-grade lung NET based on clinical behavior and underlying molecular abnormalities. This review summarizes current knowledge and challenges in the diagnosis and management of low- and intermediate-grade lung NET. Accurate histopathologic classification of lung NET is critical to determining appropriate treatment options but can be challenging even for experts. For low- and intermediate-grade lung NET, surgery remains the mainstay of treatment for localized disease. Although no standard systemic therapy has been established for the treatment of advanced, unresectable disease, a number of promising treatment options are emerging, including somatostatin analogs, temozolomide-based chemotherapy, targeted therapy with mammalian target of rapamycin or vascular endothelial growth factor inhibitors, and peptide receptor radionuclide therapy. Given the difficulty in accurately diagnosing these tumors, and the paucity of data supporting establishment of standard systemic therapy options, management of patients within the setting of a multidisciplinary team, including specialists with expertise in NET, is recommended. Ongoing and future clinical trials hopefully will provide stronger evidence to support treatment recommendations for low- and intermediate-grade lung NET.