NRTN and colonic neoplasm: Interestingly, ARTN, NRTN, GFRα1, and GFRα3 are found in colon tumors, potentially arising from gut nerves or associated with chronic inflammation of the intestine (Qiao et al., 2009; Luo et al., 2013; Han et al., 2015), which increases cancer risk, suggesting a subset of RET-expressing colon tumors may be responsive to GFL stimulation (Mendes Oliveira et al., 2018).