Enzalutamide was approved by the PBS in 2014, following the AFFIRM study, for men with castrate refractory metastatic prostate cancer who have failed treated with docetaxel due to resistance or intolerance, and who have not received or were intolerant to abiraterone. The PREVAIL study in 2014 showed enzalutamide prior to systemic chemotherapy delayed radiographic progression and improved overall survival. The PBS criteria now include those unlikely to tolerate docetaxel.
This audit was conducted to determine the tolerability and efficacy of enzalutamide in a single institution.
A retrospective chart audit was performed at the Gold Coast University Hospital for all patients treated with enzalutamide before February 2017. Baseline characteristics assessed included age, performance status, disease location and prior treatment. Outcomes assessed were toxicity, PSA response, progression-free survival and treatment after progression.
44 were identified and the median age was 70. There was a greater percentage over 75 compared to the two landmark trials (45% vs. 25%, 36%). Performance status was equivalent. 42 patients (95%) had bone metastases and only 6 (14%) had visceral disease. 16 patients (36%) had prior docetaxel with a median of 6 cycles.
The drug was well tolerated; only 15 (34%) had grade 3+ toxicity and there were no deaths due to treatment. 14 patients (32%) discontinued treatment due to adverse effects. The most common adverse events were fatigue (86%), back pain (48%) and myalgia (34%).
Median survival has not been reached. 27 (61%) had a PSA response. The median PSA progression free survival was 6.4months. 9 received subsequent chemotherapy.
Enzalutamide was generally well tolerated in a more elderly community oncology setting. There was a greater number of discontinuation of treatment due to adverse events, most commonly fatigue. The median progression free survival and PSA response rates were similar to the landmark studies.