Lung Metastases in Patients with Well-Differentiated Gastroenteropancreatic Neuroendocrine Neoplasms: An Appraisal of the Validity of Thoracic Imaging Surveillance. 
To evaluate the impact of lung metastases (LM) on overall survival (OS) in well-differentiated (WD) stage IV gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN) patients along with developing surveillance strategies for thoracic imaging.  Thirty-four patients with LM, from 3 centres, were identified (22 small intestine/12 pancreatic; 17 grade 1/15 grade 2/2 of unknown grade).  For comparison, we used 106 stage IV WD, grade 1 and 2 GEP-NEN patients with metastatic disease confined in the abdomen.  LM prevalence was 4.9% (34/692).  Eleven patients (32%) presented with synchronous LM whereas 23 (68%) developed metachronous LM at a median of 25 months (range 1-150 months).  Patients with metachronous LM had already established liver and/or para-aortic lymph node metastases.  Eighteen of 23 patients (78%) with metachronous LM exhibited concomitant progression in the abdomen.  Median OS of WD GEP-NEN patients with LM was shorter than for those with stage IV disease without extra-abdominal metastases (56 [95% CI 40.6-71.6] vs. 122.7 [95% CI 70.7-174.8] months; log-rank p = 0.001).  Among patients with progressive stage IV disease, the subset of patients with LM exhibited shorter OS (log-rank p = 0.005).  LM were also confirmed as an independent prognostic factor for survival in multivariable analysis (HR 0.18; 95% CI 0.07-0.45; p < 0.0001).  LM, although relatively rare in patients with WD stage IV GEP-NENs, may impact patients' outcome.  The development of metachronous LM is associated with concomitant disease progression in established abdominal metastases in most patients.  These patient-related parameters could be utilized for a stratified surveillance approach, mainly reserving thoracic imaging for GEP-NEN patients with progressive disease in the abdomen.