A new article has explored further previously reported observations that prostate cancer appears to occur with lower incidence in men already diagnosed as positive for human immunodeficiency virus (HIV) than in their HIV-negative, “normal” peers.
This article (by Marcus et al.) was focused, in particular, on whether it was possible to identify specific reasons for such lower incidence — including the possibility that HIV-positive men might be less frequently tested for risk of prostate cancer than their HIV-negative peers.
The study was based on data from > 200,000 men enrolled in the Kaiser Permanente (KP) health systems in northern and southern California (KPNC and KPSC, respectively), and followed from January 1, 1996 (for men in KPNC) or from January 1, 2000 (for men in KPSC) until any one of the following events:
- An initial diagnosis of prostate cancer
- Loss to follow-up
- December 31, 2007
Thus men in the KPNC health system could have been followed for up to 12 years and men in the KPSC system for up to 8 years in total.
Cancer rates by HIV status were adjusted to take account for such factors as age, race, smoking history, alcohol/drug abuse, patient weight/obesity, and diabetes. In addition, for the KPNC subset only, the authors also explored HIV status on testosterone deficiency, and on PSA testing as a proxy for cancer screening.
Here are the core study findings:
- The study included a total of 200,223 men
- 17,424 men (8.7 percent) were HIV positive.
- 182,799 men (91.3 percent) were HIV negative.
- The prostate cancer incidence rate was
- 102 per 100,000 person years among HIV-positive men (n = 74).
- 131 per 100,000 person-years among HIV-negative men (n = 1,195).
- The adjusted risk ratio (aRR) for this difference was 0.73 (P = 0.008).
- The lower risk for prostate cancer among HIV-positive men was greater for higher-stage cancers.
- Clinical identification of such higher stage tumors is less likely to be biased by screening differences than lower-stage cancers.
- Among the KPNC subset,
- More HIV-positive men (90.8%) than HIV-negative men (90.8 vs. 86.2 percent) received a PSA test by age 55 (P < 0.001).
- Decreased risk for HIV-positive men remained when examined only among those with a prior PSA test, and with adjustment for testosterone deficiency (aRR = 0.55; P = 0.001).
Marcus et al. conclude that
Prostate cancer incidence rates are lower in HIV-positive compared with HIV-negative men, which is not explained by screening differences or the risk factors evaluated.
However, at this time there seems to be no good reason to explain why men who are HIV-positive are at reduced risk for a diagnosis of prostate cancer compared to the HIV-negative population. One might reasonably have expected precisely the opposite finding. Are drugs used in the treatment of HIV capable of offering a protective effect against risk for prostate cancer … or is there some other biological effect that may underlie this reduction in risk?
Filed under: Diagnosis, Risk | Tagged: Diagnosis, HIV, risk |
THE "NEW" PROSTATE CANCER INFOLINK 
Do homosexual men have lower testosterone levels than heterosexual men? Testosterone acts as a stimulant to prostate cancer. That could be a “biological factor.”
I am not aware of any good reason to believe that homo- and heterosexual men have any differences at all in their mean testosterone levels.
Furthermore, the Kaiser database wouldn’t have been differentiating between the sexual orientations of their patients (because that would be illegal) and it is perfectly possible for exclusively heterosexual men to become HIV positive.
Although the Sitemaster is quite right to point out that HIV is a disease of all persons, it remains true that HIV-positive males are more likely than HIV-negative males to be nonheterosexual.
And there have indeed been some results indicating that testosterone levels are negative correlated with “degree” of homosexuality:
• 1971 Kolodny et al. in the New England Journal of Medicine
• 1974 Pillard et al. in Archives of Sexual Behavior
• 1977 Rohde et al. in Endokrinologie (free testosterone only)
But, naturally, other studies show no correlation. And much has changed since the 1970s.
This seems like a promising avenue for further research.
The sitemaster stands corrected … although he would note that these are very small studies from a long time ago. He would also point out that prostate cancer is not that unusual in men with hypogonadism (but the risk for prostate cancer in such men is indeed lower).
SHORTER LIFE EXPECTANCY AS A POSSIBLE EXPLANATION FOR LOWER PROSTATE CANCER INCIDENCE AMONG HIV POSITIVE MEN
I am just advancing this as a hypothesis, or perhaps just a hunch.
Clearly HIV positivity is an approximate proxy for AIDS. During the early years after the men were enrolled in the study — 1996 or 2000, depending on the division of Kaiser Permanente, survival of AIDS was not so great as I recall it. Also, AIDS tended then to be a younger person’s disease. I’m thinking that AIDS would have caused death for a substantial portion of HIV-positive men in those early years before they had a chance to be diagnosed with prostate cancer, and that could explain some of the difference in incidence. This possible explanation seems consistent with the fact that higher stage cancers take longer to develop, so early death due to AIDS might differentially pull HIV positive men out of the pool of men who were to develop higher stage prostate cancer.
Perhaps there is a way of easily testing this hunch. Just a thought: this explanation should apply to other cancers that tend to develop later in life, and we might have some statistics that are relevant about that, including a study of a basket of other cancers as a total for HIV positive versus negative men.
Dear Jim:
I am willing to be corrected by someone with real expertise on the subject of rates of HIV infection and AIDS. However, I don’t think that rates of HIV infection have been “an approximate proxy for” rates of full-blown AIDS in California for many years now. While your hunch might have been true for the 15-year period from 1980 to about 1995, it certainly wasn’t true by 2000. AIDS kills people, with an almost 100% mortality rate. By 2000, the vast majority of men with HIV did not progress to having AIDS. Prior to 1990 or perhaps even 1995, prostate cancer was almost unheard of as a significant factor in the male HIV-positive community. Why? Because no one lived long enough to even think about it as being important compared to their other clinical problems. Today, any HIV-positive male patient has very comparable risk for prostate cancer to men the HIV-negative community.