I have had a number of recent conversations with men with advanced prostate cancer who have been taking Abiraterone Acetate (Zytiga). The question that comes up in regular conversation is about knowing when Zytiga has stopped working or when Zytiga should be discontinued.
All the real guidance we have to answer this question comes from the clinical trials for Zytiga. These trials were all conducted in men with advanced prostate cancer who were both castrate resistant and had failed chemotherapy with Taxotere. In the trials Zytiga was not discontinued solely because the man’s PSA was increasing. Instead, Zytiga was considered to no longer be effective when three things happened:
1- They had a 25% increase in their PSA over the baseline which was taken at the beginning of the treatment.
2- They had radiographic evidence of disease progression as seen in a bone scan, MRI or CAT scan.
3- They had symptomatic progression as defined by the treating physician.
Zytiga was only discontinued when all three of the criteria were experienced, not because of any one of the items.
For men who have elected to use Zytiga prior to their use of chemotherapy (an increasingly common “off label” occurrence) there is no real road map to make this decision. A discussion with your doctor prior to starting Zytiga about when to discontinue should be made as you begin taking the drug. Certainly, the three criteria for the “on-label” use should be factored and given serious consideration when making this decision.
Joel T Nowak, M.A., M.S.W.