DKK1 and large cell neuroendocrine carcinoma: The bone microenvironment (the “soil”) is disrupted by vitamin D deficiency (from surgery, somatostatin analog [SSA] therapy, or steatorrhea), while high-grade lung NETs (neuroendocrine tumors) (e.g., SCLC [small cell lung cancer], LCNEC [large cell neuroendocrine carcinoma]) involve Hyaluronan-CD44, DKK1, and Annexin A1 pathways (18–21).