Low-Dose Enzalutamide in Late-Elderly Patients (≥ 75 Years Old) Presenting With Metastatic Castration-Resistant Prostate Cancer.

Background: Enzalutamide, a major antiandrogen indicated for metastatic castration-resistant prostate cancer, has worrisome toxicities in aging patients. Dose reduction might limit toxicity, but potential loss of efficacy is a concern. We compare up-front low-dose versus standard-dose enzalutamide.

Patients And Methods: Records of prostate cancer patients receiving enzalutamide were retrospectively retrieved. Selection criteria were: age ≥ 75, metastatic disease, surgical or medical castration, and rising prostate-specific antigen (PSA). Data were excluded of those missing follow-up PSA values. Low-dose enzalutamide (≤ 80 mg per day) was compared to standard dose (160 mg per day). Progression-free survival analyzed the time from start of enzalutamide to event, defined as ≥ 25% and ≥ 2 ng/mL PSA increase above nadir, or death from any cause.

Results: Fifty-nine patients were identified, of whom 16 received low-dose and 43 standard-dose therapy. Patients in the low-dose group were significantly old, with a median (range) age of 84.6 (74.9-93.8) years; median (range) PSA at start of enzalutamide was 59.2 (11.0-1058.3) ng/mL; 11 had bone metastases only, 2 metastatic lymph nodes only, and 3 bone and lymph node localizations. Pain score was > 3/10 in 4 patients (27%), Eastern Cooperative Oncology Group performance status was ≥ 2 in 9 (56%); 3 patients had received prior abiraterone and 3 bicalutamide. None received chemotherapy. PSA decrease of ≥ 50% at 12 weeks was observed in 67% patients (10/15), versus 45.0% with standard dose. Median (range) PSA at last follow-up was 1.6 (0-599.3) ng/mL. Median progression-free survival was 11.2 months, versus 11.9 months for patients receiving the standard dose (P = .612).

Conclusion: Low-dose enzalutamide in very old, symptomatic, poor-performance patients with metastatic disease was associated with high response rate and survival comparable to standard dose.