Provenge Treatment for Prostate Cancer

BY MARK SCHOLZ, MD

In 2010, Provenge was approved by the FDA, the first approved prostate cancer treatment that functions by enhancing the immune system.  Over the last couple of years Provenge has been gaining popularity with oncologists and urologists as well as with patients. What has been surprising to me is how slowly doctors and patients have warmed up to the idea of using the immune system to fight prostate cancer. For years my patients have been taking handfuls of Graviola, Shitaki mushrooms, Pau de Arco and Esiac tea because of unsubstantiated claims of immune enhancement. Yet, when the FDA approved an effective immune treatment that prolongs life I was surprised that my patients needed to be convinced to use it. 

Why, you might ask, is there any hesitation in the first place?  Well, Provenge is certainly different from other anticancer therapies at least in one very distinctive way:  Whereas the effectiveness of most treatments is signaled by a drop in PSA, PSA levels usually don’t decline after Provenge.  Having supervised more than a hundred Provenge-treated men, I have certainly seen exceptional cases with dramatic PSA declines. However, this is not the general rule. Most of the time PSA continues rising after Provenge. So people start wondering, if PSA is not dropping, how can Provenge prolong survival?  People forget that even though Provenge is administered over a six-week period, once the immune system is activated, it keeps functioning indefinitely; it’s the gift that keeps giving for the rest of your life.  Therefore, even if Provenge only slows disease growth slightly, the inhibitory effect keeps accumulating over time. So over a period of years, even a mild effect can become substantial.

If the hypothesis that Provenge is inducing a mild, long-lasting anticancer effect is correct, men take Provenge at an earlier stage (who have a longer projected survival) should receive a bigger survival benefit than men treated at a later stage. To test this thought, Dendreon, the manufacturer of Provenge, analyzed data from the original studies that led to FDA approval. Please note:  the researchers did not compare the survival of men treated earlier versus the survival of men treated later.  Obviously, men treated at an earlier stage live longer.  No, what they did is compare survival of Provenge-treated men with earlier-stage disease with similar-stage placebo-treated men.  They did the same analysis (Provenge-treated men versus placebo-treated men) in men with later-stage prostate cancer and in men with disease “in between” early and late stage.  Early stage—low-intermediate stage, high-intermediate stage and late stage—was defined by PSA levels of less than 22, 22-50, 50-134, and greater than 134 respectively. The table below summarizes the results of their analysis.

	Patients Grouped by Baseline PSA
	≤22	22–    50	50–134	>134
Number patients	128	128	128	128
Survival  months:
Provenge	41.3	27.1	20.4	18.4
Placebo	28.3	20.1	15.0	15.6
Survival Difference:	13.0	7.1	5.4	2.8

 As can be seen from the table, all groups that were treated with Provenge showed a survival advantage compared to the same stage men treated with placebo.  However, when Provenge was given at an earlier stage, the survival advantages became larger. Men with the earliest stage (PSA < 22) lived 13 months longer than similar stage men who were placebo-treated. Men with advanced stage only lived a couple months longer than advanced-stage placebo-treated men. 

This pattern of improved survival with earlier stage disease seems to fit the hypothesis that the inhibitory effect of Provenge results in a progressively longer survival when its effects are allowed to accumulate over a longer lifespan.  Based on this data one would logically conclude that Provenge induces the biggest benefits when administered at the earliest possible stage.  In the real world, where Provenge is only covered by insurance for men who are hormone resistant and have metastases, men on Lupron who have a rising PSA should be vigilantly monitored with scans such as Prostascint, C11 acetate PET and Sodium Fluoride PET scans every 6 months to detect metastatic disease at the earliest possible stage.