Supplementary Material for: Unique Metastatic Patterns in Neuroendocrine Neoplasms of Different Primary Origin

<b><i>Introduction:</i></b> Neuroendocrine neoplasms (NEN) can originate in different organs, for example, the gastroenteral tract (GE), pancreas (Pan), or lungs (L). Our aim was to examine metastatic patterns for patients with NEN of various primary origins with a special focus on brain metastases to indicate utility for screening. <b><i>Methods:</i></b> All NEN patients except for small cell lung cancer registered in the Netherlands Cancer Registry from 2008 to 2018 were selected. Metastatic patterns at initial diagnosis for NEN with different primary origins were compared. In a subcohort of patients from 2 referral hospitals (2014–2019), additional information on, for example, development of metastases after initial presentation was available. <b><i>Results:</i></b> In the nationwide cohort, 4,768/11,120 (43%) patients had metastatic disease at diagnosis (GE: 1,504/4,710 [32%]; Pan: 489/1,150 [43%]; and L: 1,230/2,978 [41%]). For GE- and Pan-NEN, the most prevalent metastatic site was the liver (25 and 39%), followed by distant lymph nodes (8 and 8%), whereas only few patients with brain metastases were identified (0% in both). In contrast, for L-NEN, prevalence of metastases in the liver (19%), brain (9%), lung (7%), and bone (14%) was more equal. In the reference network cohort, slightly more NEN patients had metastatic disease (260/539, 48%) and similar metastatic patterns were observed. <b><i>Conclusion:</i></b> Almost half of NEN patients were diagnosed with synchronous metastatic disease. L-NEN have a unique metastatic pattern compared to GE- and Pan-NEN. Remarkably, an important part of L-NEN metastases was in the brain, whereas brain metastases were almost absent in GE- and Pan-NEN, indicating utility of screening in L-NEN.