Tumor endocannabinoid levels. (A) AEA, (B) 2-AG and (C) PEA levels were measured by HPLC-MS in tumor samples of mice treated i.p. with vehicle (n = 15), PEA (n = 7), URB597 (n = 7) or both molecules co-incubation (n = 15) (at 10 mg/kg/day, daily) for six days. Basal levels are 78.4 ± 11.7 pmol/g, 1.55 ± 0.11 nmol/g and 546.1 ± 55 pmol/g of tissue for AEA, 2-AG and PEA, respectively. Significantly different (**P < 0.01) from vehicle administration.