Flt3L mRNA expression was evident in all NEN tumor samples, whereas the tissue mRNA transcripts for GM-CSF were below the detection limits of our RNAseq approach in 19/22 samples from the high-grade cohort (41/47 in the combined cohort), indicating that circulating GM-CSF reflects its production at extratumoral sites, such as the bone marrow. The gene discussed is CSF2; the disease is neoplasm.