Provenge and Zytiga Facts
The Provenge and Zytiga facts are good to know when trying to make a decision about treatment for metastatic prostate cancer. The pharmaceutical industry is highly competitive, and the players come out of their corners fighting full force when the stakes are high. Currently, two competitors in the arena for the metastatic hormone resistant prostate cancer market are Provenge (sipuleucel-T) and Zytiga (abiraterone), but the competitors are not evenly matched.
Let’s look at some Provenge and Zytiga facts. First of all, the two drugs are not in the same drug class. Provenge, made by Dendreon, is a form of immunotherapy and the only drug for advanced prostate cancer that can make this claim. It is sometimes referred to as a vaccine for treatment of prostate cancer and is also the only immunotherapy drug approved by the Food and Drug Administration (FDA) for treatment of advanced prostate cancer.
Zytiga also has a unique quality in that it is the only hormone therapy drug that stops hormone production in three sites: the testes, adrenal glands, and the prostate tumor itself. Other hormone therapies for prostate cancer are capable of interfering with hormone production in the first two mentioned sites only.
Among other Provenge and Zytiga facts is the announcement by Johnson & Johnson (maker of Zytiga) that it was stopping its latest trial because the drug had (1) demonstrated good control of prostate-specific antigen (PSA) levels (an indicator of disease progression), and (2) shown a trend for an overall survival benefit. While the first factor is significant, the second is not because the trial results did not demonstrate a statistically significant improvement in overall survival, which was one of the two main endpoints of the study.
Why is this important? Because J&J indicated that the Zytiga trial had been a success, yet according to the rules regarding medical trials, all defined endpoints must be statistically significant before a trial can be deemed a success.
That’s not to say that Zytiga is not effective for treatment of late-stage prostate cancer –that remains to be determined. However, it appears the drug was not given a full opportunity to prove itself in this latest trial.
Provenge, on the other hand, recently met its study endpoint (overall survival). The clinical trial involved 512 men, and the median survival for the 341 men who took Provenge was 4.1 months longer than that of the 171 men who were in the placebo group.
More specifically, men in the Provenge group lived a median of 25.8 months compared with 21.7 months in the control group. Furthermore, at three years, 37.8% more men treated with Provenge were alive when compared with men in the control group.
More Provenge and Zytiga Facts
When the results of the Provenge trial are compared with those of the Zytiga trial, we find that:
- Provenge showed a statistically significant benefit in overall survival that also improved over time
- The benefit in overall survival seen with Provenge was clear at six months after treatment
- Zytiga did not show a benefit in overall survival until 18 months after the men started treatment. By that time, 20% of the men being treated had died, before any possible survival benefit was apparent
Other Provenge and Zytiga facts concerning treatment:
- Provenge requires three doses given over 4 to 5 weeks and then the treatment is done
- Zytiga must be taken daily, along with a steroid (prednisone), for an average of eight months. Steroids weaken the immune system, which places the patient at increased risk of infection, while Provenge works with the immune system
- Because men who wish to take Provenge must be free of steroid use (via a steroid wash out waiting period) before they begin treatment, men who have already used Zytiga must go through this wash out period before they can start Provenge. Given the importance of treating men who have metastatic hormone resistant prostate cancer as promptly and effectively as possible, this wash out period could prove deadly for some men. In addition, men are eligible for Provenge only if their disease is asymptomatic or minimally symptomatic. Men who need to wait throughout a steroid wash out period are likely to progress past this stage of disease, making them ineligible for Provenge.
Men with metastatic hormone resistant prostate cancer need to educate themselves about Provenge and Zytiga facts and discuss them thoroughly with their healthcare providers before making a treatment decision.