FAAH and breast cancer: Supporting our previous data showing an association between FAAH and luminal BC phenotypes, the expression of both isoforms of ER (Esr1 and Esr2) was downregulated in tumors from MMTV-neu:FAAH−/− mice compared to FAAH+/+ controls, while the basal marker cytokeratin 5 (Krt5) was upregulated (Fig. 3h).