NTRK1 and neoplasm: Nerve growth factor (NGF) from cancer cells causes increased nerve density in the tumor microenvironment (Rowe et al., 2020), while nerve cells expressing nerve growth factor (NGF) receptors of NTRK1 (TRKA) and NGFR (p75NTR) were found, and it was thought that there was a correlation between a large amount of NGF produced by cancer cells and the presence of nerves (p = 0.02) (Griffin et al., 2020).