ESR1 and neoplasm: In fact, a correlation has been established between CB2 expression and tumor aggressiveness, as mRNA CB2 levels were higher in ER−/PR− tumors than in ER+/PR+ tumors, as well as in HER2+ tumors than in HER2− tumors, and in high-grade histological tumors than in low-grade histological tumors [10,91].