New Insights into the Molecular Characteristics of Pulmonary Carcinoids and Large Cell Neuroendocrine Carcinomas, and the Impact on Their Clinical Management

Carcinoids and large cell neuroendocrine carcinomas (LCNECs) are rare neuroendocrine lung tumors. Here we provide an overview of the most updated data on the molecular characteristics of these diseases. Recent genomic studies showed that carcinoids generally contain a low mutational burden and few recurrently mutated genes. Most of the reported mutations occur in chromatin-remodeling genes (e.g., menin 1 gene [MEN1]), and few affect genes of the phosphoinositide 3-kinase (PI3K)-AKT-mechanistic target of rapamycin gene pathway. Aggressive disease has been related to chromothripsis, DNA-repair gene mutations, loss of orthopedia homeobox/CD44, and upregulation of ret proto-oncogene gene (RET) gene expression. In the case of LCNECs, which present with a high mutation burden, two major molecular subtypes have been identified: one with biallelic inactivation of tumor protein p53 gene (TP53) and retinoblastoma gene (RB1), a hallmark of SCLC; and the other one with biallelic inactivation of TP53 and serine/threonine kinase 11 gene (STK11)/kelch like ECH associated protein 1 gene (KEAP1), genes that are frequently mutated in NSCLC. These data, together with the identification of common mutations in the different components of combined LCNEC tumors, provide further evidence of the close molecular relation of LCNEC with other lung tumor types. In terms of therapeutic options, future studies should explore the association between mechanistic target of rapamycin pathway mutations and response to mechanistic target of rapamycin inhibitors in carcinoids. For LCNEC, preliminary data suggest that the two molecular subtypes might have a predictive value for chemotherapy response, but this observation needs to be validated in randomized prospective clinical trials. Finally, delta like Notch canonical ligand 3 inhibitors and immunotherapy may provide alternative options for patient-tailored therapy in LCNEC.