HCRTR1 and malignant colon neoplasm: It should be noted that endogenous OxA had no intrinsic action on tumor development because: 1) no OxA/OxB peptides were detected in the tumor environment (68); 2) the circulating level of OxA was very low (about 60 pM) does not allow OX receptors activation which displayed a 5-10 nM range of affinity (77); and 3) xenografted tumors developed from colon cancer cell line which does not express OX1R, shown a similar development kinetic that colon cancer cells expressing OX1R (68).