Incidence of prostate cancer is significantly lower among men living with HIV, investigators from California report in the online edition of the Journal of Acquired Immune Deficiency
“We found a 27% reduced risk of prostate cancer among HIV-positive men
after adjustment,” comment the authors. “HIV-positive men were more likely to
be tested and were diagnosed with lower-stage cancers and lower PSA [prostate
Thanks to antiretroviral therapy, an ever-increasing proportion of people
with HIV are now living into older age. The diseases of ageing are therefore an
increasingly important cause of illness among people living with HIV. For instance,
diagnoses of prostate cancer increased fivefold among men living with HIV in the
US between 1991 and 2005. Despite this, infection with HIV has been associated
with a 20 to 25% reduction in the risk of being diagnosed with prostate cancer. It has been
suggested that this is due to lower screening rates.
Investigators from Kaiser Permanente in California wanted to see if
infection with HIV really was associated with a reduced risk of being diagnosed with prostate cancer
and if this could be attributed to lower levels of PSA screening.
They therefore designed a case-controlled study matching each
HIV-positive participant with ten HIV-negative controls who entered care in the
same year, were of a similar age and were receiving care at the same centre.
Incidence of prostate cancer was compared between the HIV-positive and
HIV-negative men, adjusting for potential confounders such as age, race,
smoking, drug or alcohol use, diabetes and testosterone levels.
Data were also collected on rates of PSA screening for men enrolled
in Northern California.
Study participants entered care after 1996 (Southern California) or 2000 (Northern
California). The study population included 17,424 HIV-positive and 182,799
HIV-negative men. They were followed for a mean of 4.2 and 5.0
person-years/subjects, respectively. The groups were of similar age. However,
the men living with HIV were more likely than the HIV-negative men to be white and to
report a history of smoking (39 vs 23%), alcohol abuse (12 vs 7%), drug
abuse (15 vs 4%) and testosterone deficiency (13 vs 1%). Prevalence of
diabetes and obesity did not differ by HIV status.
Almost two-thirds of HIV-positive men (62%) were in the men who have sex
with men (MSM) risk group. Only 42% of the men living with HIV were taking
antiretroviral therapy at the time they entered the study. By the end of
follow-up, 76% were taking HIV treatment, mean CD4 count was 466 cells/mm3
and 61% had a viral load below 500 copies/ml.
Prostate cancer was diagnosed in 74 HIV-positive and 1195 HIV-negative
men. Differences according to HIV status were observed. Men living with HIV were
more likely to be diagnosed with less advanced cancers (state II, 95 vs 89%;
stage III-IV, 5 vs 11%) and to have localised (93 vs 83%) rather than
regional/distal (3 vs 14%) cancers. Recent PSA levels were lower among men living with HIV (10 vs 17).
Overall incidence of prostate cancer was 102/100,000 person-years for
men living with HIV compared to 131 per 100,000 person-years for HIV-negative men. After
controlling for potential confounders, men living with HIV had a 27% reduction in the
risk of prostate cancer (RR = 0.73; 95% CI, 0.57-0.92). The association between
HIV infection and a reduced risk of prostate cancer was strongest for more
advanced cancers (stage III/IV, RR = 0.28; 95% CI, 0.009-0.90; regional/distal
cancers, RR = 0.28; 95% CI, 0.11-0.68). However, men living with HIV also had a
reduced risk of less severe forms of cancer (stage II, RR = 0.77; 95% CI,
0.60-1.01; localised cancers, RR = 0.81; 95% CI, 0.63-1.05).
These differences could not be explained by lower levels of screening
among men living with HIV. In fact, a higher proportion of HIV-positive than
HIV-negative men had undergone PSA screening by the age of 55 (91 vs 86%, p
The investigators restricted their analysis to the sub-set of men in
Northern California who had PSA testing. After adjustment, men living with HIV had
a significantly reduced risk of prostate cancer (RR = 0.55; 95% CI, 0.39-0.80).
“Our results suggest that the observed lower incidence of prostate caner
among HIV-positive men…is attributable to factors other than differences in PSA
screening,” comment the investigators.
No HIV-related characteristics were associated with prostate cancer
risk. For both HIV-positive and HIV-negative men, risk of the cancer increased
with age (p < 0.001) and was also associated with black vs white ethnicity.
The investigators call for further research to investigate why
men living with HIV have a lower risk of prostate cancer.