The treatment landscape for metastatic prostate cancer is shifting and expanding yet again, according to new findings from two large clinical trials presented at the 2019 annual meeting of the American Society of Clinical Oncology (ASCO). The ENZAMET trial tested the drug enzalutamide (Xtandi) and the TITAN trial tested apalutamide (Erleada) in men whose cancer is still responsive to hormone-suppressing therapies—also called castration-sensitive prostate cancer. In both trials, combining the respective drugs with the androgen deprivation therapy (ADT) substantially improved how long men lived overall and how long they lived without their cancer getting worse.
The ENZAMET trial enrolled more than 1,100 men with hormone-sensitive metastatic prostate cancer. The men were randomly assigned to ADT combined with enzalutamide or with any of three other androgen-blocking drugs. At a median follow-up of nearly 3 years, men who received ADT plus enzaluatamide had a 33% reduced risk of death, with 80% still alive compared with 72% of men treated with ADT plus another antiandrogen drug. Men in the enzalutamide group also had better clinical progression-free survival (PFS), which the research team defined as the time until the return of disease-related symptoms, the detection of new metastases on imaging scans or the initiation of another cancer treatment for prostate cancer, whichever came first. At 3 years, 63% of men in the enzalutamide group were alive without clinical progression of their disease, compared with 33% in the standard treatment group. Although enzalutamide appeared to be effective regardless of whether men had high- or low-volume disease, one apparent differentiating factor was planned early treatment with docetaxel (taxotere). Nearly half of the men in both treatment groups received early treatment with docetaxel and, for those men, enzalutamide was not associated with longer overall survival.
From the standpoint of efficacy, similar results were seen in the TITAN trial with apalutamide (Erleada). Funded by the drug’s manufacturer, Janssen Pharmaceuticals, the trial enrolled more than 1,000 men with hormone-sensitive, metastatic prostate cancer, with participants randomly assigned to receive ADT along with a placebo or ADT plus apalutamide. At 2 years of follow-up, approximately 82% of men who received ADT plus apalutamide were still alive compared with 74% in men treated with ADT plus placebo, for a 33% reduction in the risk of death. The trial’s other primary measure was the amount time men lived without evidence on imaging scans that their disease had progressed, known as radiographic PFS. At a median follow-up of nearly 2 years, men treated with ADT plus apalutamide had a 50% improvement in radiographic PFS than men treated with ADT alone.
What factors would influence the choice of treatments? In the case of enzalutamide and apalutamide, Dr. William Dahut, clinical director of the National Cancer Institute’s Center for Cancer Research said, both drugs “may be particularly good choices for men with low-volume disease, who might shy away from docetaxel” due to concerns about side effects. Unlike docetaxel, which must be administered intravenously in the hospital, enzalutamide, apalutamide, and abiraterone are oral drugs that can be taken at home, so they also offer greater convenience for patients. On the other hand, many patients tolerate docetaxel quite well, Dr. Dahut noted, and it’s given for a fixed duration, not continuously like the other drugs. Other factors such as insurance costs may also affect treatment choice.
For additional details, see the following article published June 19th, 2019 on line by the National Cancer Institute (NCI) Cancer Currents Blog.