Deep and Ongoing Response of Castrate-Resistant Prostate Cancer on Very Low-Dose Enzalutamide in an Elderly Chemotherapy–naïve Patient: a Case Report

Background Enzalutamide is an orally administered drug that blocks signaling in the androgen receptor with clinical activity in both chemotherapy–naive and post-chemotherapy patients with castrate-resistant prostate cancer (CRPC). Enzalutamide is generally well-tolerated, but dose reductions are nonetheless needed in case of side effects. Case An 82-year-old patient with chemotherapy–naive metastatic castration-resistant prostate cancer was treated with a very low dose of 40 mg enzalutamide once daily. The trough levels of enzalutamide and the active metabolite N-desmethylenzalutamide were 4.5 mg/L and 3.0 mg/L, respectively. This exposure provided a long-term response without any significant side effects. Conclusion Low doses of enzalutamide may be efficacious, while also reducing the risk of side effects. Furthermore, employing a lower dose would reduce healthcare costs and increase access to enzalutamide. Studies exploring the efficacy of lower enzalutamide doses are warranted.