Efficacy and Tolerability of Low-Dose Enzalutamide in Prostate Cancer

Prostate cancer is the most frequent cancer in males in the United States, with 299.000 new cases estimated in 2024, and it is the second leading cause of cancer-related death in men. Since 2014, the prostate cancer incidence rate has risen by 3% per year, mostly driven by 4-5% per year increases for regional-stage and distant-stage diagnoses that began as early as 2011. Localized-stage disease also increased from 73.5 per 100.000 in 2014 to 84.8 per 100.000 in 2019, although the trend is not yet statistically significant. A recent study estimated that more than one half of men in the United States living with metastatic prostate cancer were initially diagnosed with localized or regional stage disease. In Italy, there were more than 41.000 diagnosed cases in 2023 and 8.200 deaths, accounting for nearly one-fifth of all cancers detected in men, and over 560.000 prevalent cases of men living with prostate. Enzalutamide is a new generation oral androgen-receptor selective inhibitor that induces tumor regression and growth suppression in patients with metastatic prostate cancer. It is effective and well tolerated, compared with other anticancer drugs (ex-chemotherapy), but in real practice, very often in patients with comorbidity or poor performance status is necessary reduce the dose to reduce fatigue or other adverse events. The standard recommended dosage of 160 mg per day has multiple side effects and dose reductions are often required. Several randomized studies have underscored the importance of enzalutamide in treating prostate cancer. Initially approved by the Food and Drug Administration in 2012 for patients with metastatic castration-resistant prostate cancer who had previously received docetaxel, its indications were updated in October 2020 to include patients with castration-resistant prostate cancer experiencing biochemical relapse, or with metastatic castration-sensitive prostate cancer. In phase I study enzalutamide (MDV3100) was administered with dose between 30 and 600 mg per day. There was a linear increase in steady state serum concentration with dose, but antitumor effects were observed at all doses, including 40-60 mg per day. The severity of treatment related adverse effects including fatigue and neurological disorders was associated with drug dose. Recent data suggest its efficacy may be retained at lower doses with significant improvement in safety and tolerability. In two previously observational studies, in metastatic prostate cancer low-dose enzalutamide (≤ 80 mg per day) compared to standard dose (160 mg per day) did not show difference in overall survival and prostate-specific antigen progression-free survival. Interestingly, there was a trend towards a better prostate-specific antigen response and a significantly longer life among the low-dose group.