Sometime this week, the first therapeutic vaccine for cancer is going to be approved by the FDA to treat prostate cancer. The vaccine, Sipuleucel-T, is being marketed by Dendreon as Provenge. The company has shown that the vaccine extends the lives of advanced prostate cancer patients by an average of 4.5 months. Some of the participants in the trial lived for an additional 2-3 years. The side effects observed in the clinical trials were limited to mild flu-like symptoms—a key advantage to Provenge over conventional therapies.
It is being reported that the vaccine will cost approximately $75,000 per patient. When I first read this, sadly, I wasn’t shocked. I had just read an article in the Washington Post by Sandra G. Boodman that told the story of three different cancer patients who had to decide between dying of their cancer or putting their families into debt to pay for their cancer medications. One patient’s insurance company refused to pay for an oral chemotherapeutic medication ($4000 per month) when the i.v. version was cheaper. The patient had surgery to implant a port into her chest for the i.v. When the port sprang a leak, she was rushed to the ER. She bitterly remarks that if the insurance company had paid for the pill version of the drug, it would have been less expensive than the surgery and ER visit, and she is probably correct. This article went on to talk about another man with a form of leukemia that filled a prescription for the drug Gleevec at his pharmacy. The total charge was $10,000 for a 30-day supply. In her article, Boodman uses these stories to frame her report on the greed of pharmaceutical companies and the lack of federal guidelines and legislature that addresses these very real financial issues that are literally forcing people to choose between dying or diving into deep financial ruin in order to live. Of course, the companies cite that the development of these drugs cost billions and years to gain FDA approval. They legitimately have a lot invested and do deserve to profit off of these drugs. I have hard time reconciling the needs of the patient and the rights of the companies. I know that it can take about 10 years and about $1 billion for a drug to be developed, tested, approved, and marketed. It is a significant investment on the part of the company, which includes not only the individuals on the business end, but also scientists and doctors who literally devote their entire careers. The companies like to site that they have programs to cover the costs for patients who can’t afford their treatment. While this is an outstanding service that they provide to their community, many patients will never know about this option or live long enough to maneuver their way through the paperwork.
While Gleevec and other drug therapies simply require the patient to take a pill, Provenge is unique. It is not a pill. Actually, it isn’t a drug at all. Patients undergo leukapheresis, a procedure in which blood is collected and the white blood cells are separated out. These white blood cells include antigen-presenting cells (APCs). APCs are immune cells responsible for the recognition, processing and presentation of foreign antigens to the T-cells. The APCs are sent to a Dendreon facility, where they are kept alive in culture and exposed to a recombinant fusion protein that contains prostatic acid phosphatase (PAP). PAP is an enzyme produced by the prostate and found at elevated levels in the blood of prostate cancer patients, much like prostate-specific antigen (PSA), because the cancer cells produce it and it sheds from the cell surface into the blood stream. Cancer cells have multiple mechanisms by which they can avoid detection by T-cells. The APCs process and present PAP on their surface. Two days after the initial blood draw, the patient returns to the hospital/doctor’s office and the APCs are infused back into their body through an i.v. They undergo this process three times over the course of a four-week period and then the treatment is complete. The PAP-presenting APCs interact with other types of immune cells in the body. Essentially, the APCs are “telling” your T-cells that the PAP protein is “bad” so that they target and kill any cells in the body that express this protein on their surface. The result is that your own immune system is manipulated and used to kill your cancer. It is unlike any other FDA-approved cancer therapy. Every man diagnosed with prostate cancer will undergo this treatment, just as chemotherapy and hormone therapy are the standard today. For these men, the key will be how they pay for it.
From this point on, labs will be writing clinical trials for prostate cancer that will combine their drug with Provenge, as it will eventually become the standard of care for metastatichormone-refractory prostate cancer. This will undoubtedly be a complex undertaking as the workings of the immune system are intricate and easily influenced. It is well established that some chemotherapy drugs are immunosuppressive. It is reasonable to question if other drugs will effect the immune system’s ability to respond to Provenge or some other therapeutic vaccine. This is a question that I ask everyday in my own studies. Clearly, this is a truly exciting development that will benefit patients. However, the FDA approval of the first therapeutic vaccine for prostate cancer is also a significant event for the field of cancer biology. It is going to create an unbreakable bridge between the fields of immunology and cancer biology and will hopefully encourage the development and approval of future innovative immunotherapeutic approaches to treat cancer, leading to treatment options for patients with fewer side effects and better outcomes.
