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Mistaken Judgment:  Prostate Cancer Hormone Treatment(V)

Feature Article Mistaken Judgment: Prostate Cancer Hormone TreatmentV
AUG 18, 2017 LISTEN

The Paradox Resolved
Still, I was worried, because there was a bothersome unresolved paradox to explain. For decades, the storyline was that lowering testosterone levels caused prostate cancer to shrink away and raising testosterone levels caused it grow. The second part of this story was now seriously in doubt, yet the first part was obviously correct. In my own practice, I had seen the beneficial effects of lowering testosterone levels many times over in men with advanced prostate cancer. This part of Dr. Huggins’s work was indisputable. But if lowering testosterone levels caused these cancers to shrink, how was it possible that raising testosterone levels did not cause the cancers to grow? This was a paradox that needed to be solved if physicians were to accept the possibility that testosterone therapy may not increase the risk of prostate cancer.

The answer turns out to be not all that complicated. All the reports of testosterone causing rapid growth of prostate cancer occurred in men who already had extremely low testosterone levels, due to castration or estrogen treatment. Once we get beyond the near-castrate range, it is hard to find any evidence that changes in T concentrations matter at all to prostate cancer. This is essentially what Drs. Fowler and Whitmore described in their 1981 article when they suggested that “near maximal” growth of prostate cancer is provided by naturally occurring T concentrations.

The experimental proof of this concept was provided by a landmark article published in 2006 using much more sophisticated means. In this study by Leonard Marks and colleagues, men with low testosterone received injections of testosterone or a placebo every two weeks for a total of six months. At the beginning and end of the study, measurements of testosterone and DHT (the more active form of testosterone within prostate tissue) were obtained from the blood and also from the prostate itself. The results showed that although blood concentrations of testosterone and DHT rose substantially in the T injection group, as expected, the concentration of testosterone and DHT within the prostate itself did not change at all and was similar to the group that received placebo injections. In addition, biochemical markers of prostate cell growth also did not change with T injections.

This study showed in elegant fashion that raising testosterone levels in the blood did not raise testosterone levels within the prostate. It is as if once the prostate has been exposed to enough testosterone, any additional testosterone is treated as excess and does not accumulate in the prostate. In technical terms, we say the prostate has been saturated with regard to testosterone. And it is this saturation that resolves the paradox of testosterone and prostate cancer.

Saturation explains the paradox in this way. At very low levels of T, near the castrate range, prostate growth is very sensitive to changes in T concentration. Thus, severely lowering testosterone will definitely cause prostate cancer to shrink; adding testosterone back will cause the cancer to regrow. However, once we get above the point where the prostate is saturated with testosterone, adding more testosterone will have little, if any, further impact on prostate cancer growth. Experimental studies suggest the concentration at which this saturation occurs is quite low.

In other words, the old analogy I learned in training was false. Testosterone is not like food for a hungry tumor. Instead, a much better analogy is, “Testosterone is like water for a thirsty tumor.” Once the thirst has been satisfied, prostate tumors have no use for additional testosterone. And the vast majority of men with low testosterone appear to have prostates that are not particularly thirsty.

A New Concern: Prostate Cancer and Low testosterone

I no longer fear that giving a man testosterone therapy will make a hidden prostate cancer grow or put him at increased risk of developing prostate cancer down the road. My real concern now is that men with low testosterone are at an increased risk of already having prostate cancer.

When my colleagues and I published our results in 1996 from prostate biopsies in men with low testosterone and PSA of 4.0 ng/mL or less, the 14 percent cancer rate was several times higher than any published series of men with normal PSA. In 2006, Dr. Rhoden and I published a larger study of prostate biopsies performed in 345 men. The cancer rate of 15 percent in this group was very similar to the first study. But whereas the cancer rate in 1996 was much higher than anything published to that date in men with PSA of 4.0 ng/mL or less, in 2006 the perspective had changed due to an important study called the Prostate Cancer Prevention Trial.

In that study, the cancer rate among men with a PSA of 4.0 ng/mL or less was also 15 percent. Because this value is identical to what we had found in our patients with low testosterone, it was suggested that the cancer rate in men with low testosterone is the same as the normal population—neither higher nor lower. However, the average age of men in our study was a decade younger than the men studied in the Prostate Cancer Prevention Trial (fifty-nine versus sixty-nine years). Almost half the men in the other study were seventy years or older, and age is the greatest risk factor we know for prostate cancer. The way I look at these numbers is that men with low testosterone have a cancer rate as high as men with normal T who are a decade older.

More importantly, in our study of 345 men, we found that the degree of testosterone deficiency correlated with the degree of cancer risk. Men whose testosterone levels were in the bottom third of the group were twice as likely to have cancer diagnosed on biopsy as men in the upper third. This finding adds to the concern that low testosterone is a risk factor for prostate cancer.

There is now additional data from around the world associating low testosterone and worrisome features of prostate cancer. For example, low testosterone is associated with more aggressive tumors. In addition, men with low testosterone appear to have a more advanced stage of disease at the time of surgical treatment.

Whereas I originally began to perform prostate biopsies in men with low testosterone because I was worried that treatment might cause a hidden cancer to grow, I now perform biopsies in these men because I am concerned they might have an increased risk of cancer. This risk is approximately one in seven for men with PSA values less than 4 ng/mL.

Because prostate cancer tends to be curable when caught early, I feel I’ve done these men a service by finding their cancers before they have an abnormal PSA or DRE. With today’s ability to monitor men with prostate cancer, not all of these men will necessarily require treatment. But the ones who have evidence of more aggressive tumors should definitely have an advantage by having their diagnosis made early.

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