Abiraterone Acetate (Zytiga) Approved to Treat Hormone-Refractory Prostate Cancer Before Chemotherapy.

In the past, when a prostate cancer patient became non-responsive (refractory) to hormonal therapy, the next step in his treatment was chemotherapy with taxotere (docetaxel). This treatment was usually accompanied by significant side effects.  Meanwhile, in April, 2011, the Food and Drug Administration (FDA) had initially approved abiraterone acetate (Zytiga) for use in patients whose prostate cancer had progressed after chemotherapeutic treatment with taxotere.  But on December 10th, 2012, the FDA  expanded the approved use of abiraterone before chemotherapy for men with hormone-refractory, metastatic prostate cancer.
Testosterone stimulates the growth of prostate tumors, so drugs such as Lupron used in hormonal therapy or surgery that reduces testosterone production or blocks testosterone’s effects are used to slow the growth of prostate cancer. However, most prostate cancers eventually become resistant to these treatments. These resistant cancers continue to grow even when levels of testosterone are very low. Abiraterone is a pill that treats tumors by reducing testosterone production by inhibiting the production of androgen (testosterone) in the testes, adrenal glands, and prostate cancer tumors themselves.

Abiraterone’s safety and effectiveness for its expanded use were established in a clinical study of 1,088 men with late-stage, hormonal-resistant prostate cancer who had not previously been treated with chemotherapy. Participants received either abiraterone or a placebo (both in combination with the corticosteroid prednisone). The study was designed to measure the length of time a patient lived before death (overall survival) and the length of time a patient lived without further tumor growth as assessed by imaging studies (radiographic progression-free survival, or rPFS).  Patients who received abiraterone had a 25 percent decrease in the risk of death. Study results also showed abiraterone improved rPFS. The median rPFS was 16.5 months for patients treated with abiraterone versus 8.3 months in the placebo group.

The most common side effects reported included fatigue, joint swelling or discomfort, swelling caused by fluid retention, hot flashes, diarrhea, vomiting, cough, high blood pressure, shortness of breath, urinary tract infection, and bruising.  The most common laboratory abnormalities included low red blood cell count; high levels of the enzyme alkaline phosphatase, which can be a sign of other serious medical problems; high levels of fatty acids, sugar, and liver enzymes in the blood; and low levels of lymphocytes, phosphorous, and potassium in the blood. For further information, see the FDA update section in the December 11th, 2012 issue of the National Cancer Institute (NCI) Bulletin. 

In the last weeks, information about the use of Zytiga has been published in several sources. Among them, the Prostate Cancer Foundation (PCF) Newsletter of December 19th, 2012 described the approval of Zytiga as one of the main breakthroughs of 2012. The December 13th, 2012 edition of the ZeroHour Newsletter (from Zero-The Project to End Prostate Cancer) also reprinted an article about approval of Zytiga. Finally, the news was also published in the Dec. 13th issue of the Prostate Cancer Research Institute (PCRI) Weekly.