A promising treatment for hormone naive prostate cancer

The objective of this study was to determine if enzalutamide (Xtandi) is both safe and effective in patients with prostate cancer not previously treated with hormone therapy.  

Androgen-deprivation therapy (ADT) is one of the main treatments for advanced prostate cancer. Many ADT drugs can lower levels of testosterone and estrogen (sex hormones) in the body, causing side effects such as decreased bone strength. Enzalutamide is an ADT drug that does not work by decreasing levels of hormones in the body. Instead it blocks the hormones from interacting with proteins on the cell surface, the method by which hormones usually cause their effects. Due to the fact that the levels of hormones remain the same, this reduces the impact on bone strength.

The 67 patients in this trial had prostate cancer that had not previously been treated with hormone therapy. Patients had testosterone levels greater than 230 ng/dl. Both patients with confined cancer and cancer that had spread to distant sites in the body (metastasis) were included. The patients were reviewed after 1 year (54 patients still taking the drug) and again after 2 years (45 patients still taking the drug).

The results showed that enzalutamide caused a large and consistent reduction in prostate-specific antigen (PSA: a protein elevated in the presence of cancer) levels in 100% of patients who were still taking the drug at 1 year and 2 years. Average PSA levels at 1 year were 0.54 ng/ml and at 2 years were 0.16 ng/ml.

Patients that entered the study with metastases showed the most promising results at 2 years. 50% of these patients experienced complete disappearance of signs and symptoms of the cancer while 15% experienced partial disappearance of signs and symptoms.

Overall, there was a small decrease in bone density of 3%. Some hormone levels, such as testosterone, increased throughout the study. The most frequent treatment-related adverse events were enlargement of the breast tissue (gynecomastia; 49%), fatigue (39%), nipple pain (21%) and hot flushes (21%). There were 5 serious drug-related events; 4 involved abnormal beating of the heart and one involved chronic fatigue.

The authors concluded that enzalutamide appeared to be effective in the treatment of prostate cancer that has not been treated previously with hormone therapy, with less of a decrease in bone density than usually seen with ADT. 

There was a small group participating in this study and there was no group for comparison.