Abstract: Breast cancer is the most common cancer diagnosed in women and the second most common cause of death from cancer among women worldwide. Hormonal therapy with tamoxifen is the primary option for estrogenic receptor-positive patients. However, tamoxifen's effectiveness could be significantly influenced by drug metabolism through the CYP2D6 enzyme. The concomitant use of drugs that inhibit this enzyme can decrease the conversion of tamoxifen to its active metabolite, Endoxifen, thereby reducing therapeutic efficacy. Ficus deltoidea, a native Indonesian plant, is known to possess antioxidant and antiproliferative properties and may be potentially developed as an adjuvant in cancer therapy.