Men living with HIV have a lower risk of prostate cancer

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 Syndromes.

“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 specific antigen].”

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 < 0.001).

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.