In a study investigating the effects of ∆9-THC in a murine model of mammary carcinoma, it was found that the murine mammary carcinoma cell line 4T1 first did not express detectable levels of the cannabinoid receptors CB1 and CB2 and second, these cells were resistant to the cytotoxicity of ∆9-THC. This evidence concerns the gene CNR1 and breast carcinoma.