When men with advanced prostate cancer first become castrate resistant (their prostate cancer continues to grow as evidenced by an increasing PSA and or by disease progression on scans), they usually add either abiraterone acetate (Zytiga) or enzalutamide (Xtandi) to their hormone therapy treatment (ADT). These second-line drugs, Zytiga and Xtandi, are not used in place of the ADT, but along with the ADT therapy.
Why are Zytiga and Xtandi added to ADT and not substituted for ADT?
ADT is designed to stop the production of the testicular androgens which account for a large portion of all the androgen production in the male body. However, additional androgen production continues from the adrenal glands as well as from the prostate cancer cells! ADT does not stop the androgen production from the adrenal glands and the cancer cells, but through the development of mutations in the cancer cells, can support the growth of the prostate cancer despite a man being castrated.
By adding Zytiga or Xtandi to the ADT protocol when a man becomes castrate resistant, the prostate cancer will usually positively respond because it is then denied both the testicular and the adrenal androgens.
Stopping ADT when adding Zytiga or Xtandi will allow the testicular androgens to be again manufactured and then support the growth of the prostate cancer.
By Joel T Nowak, MA, MSW