Early detection of prostate cancer has led to a reduction in the number of men with metastatic cancer over time, researchers found in a population-based study analyzing patients in the U.S. and Denmark.

The study findings were presented at the European Association of Urology Congress 2018 (EAU2018) in Copenhagen, Denmark, in a lecture titled “Incidence and survival trends of de-novo metastatic prostate cancer – a population-based analysis of two national cohorts from USA and Denmark”.

The team analyzed metastatic prostate cancer incidence in two large groups of patients from the U.S. and Denmark: 29,555 men registered at the Surveillance, Epidemiology and End Results (SEER), and diagnosed from 1980 to 2011, and 6,874 men included in the Danish Prostate Cancer Registry (DaPCaR), and diagnosed from 1995 to 2011.

Patients were grouped according to the time they were diagnosed, and each group was analyzed separately and compared to the others.

In the SEER group, the largest and longest one, the incidence of metastatic prostate cancer dropped from 12.0 cases per 100,000 men from 1980 to 1984, to 4.4 cases per 100,000 men from 2005 to 2011.

Contrarily, the Danish DaPCaR group revealed an increase from 6.7 cases per 100,000 men from 1995–1999, to 9.9 per 100,000 from 2005–2011.  

Although these results might seem to be contradictory, the decline in metastatic disease observed in the American population is expected to be the case in Denmark in the relatively near future, researchers predict.

“Our findings from the US population suggest that prostate cancer-specific mortality is highly affected by the incidence of de novo metastatic disease. If the patterns of incidence continue to mimic the American [data], a drop in prostate cancer-specific mortality might be anticipated in Denmark within a few years,” Thomas Helgstrand, MD, PhD, said in a press release. Helgstrand, of the Copenhagen Prostate Cancer Center, is first author of the study.

In fact, DaPCaR data revealed a significant decline in the 5-year prostate cancer-specific mortality from 73.4% in 1995–1999, to 56.8% in 2005–2009. This was accompanied by a significant decrease in levels of prostate-specific antigen (PSA) at diagnosis (from 320 to 145 ng/mL). The overall 5-year prostate cancer-specific mortality rate was 64%.

The reduced mortality over time in the DaPCaR is attributed by researchers to an increase in men diagnosed early for prostate cancer.

SEER findings show a total 5-year prostate cancer-specific mortality rate of 56%, which increased slightly from 54.2% in 1980–1984, to 61% in 2005–2009.

The overall lower rate of prostate-associated mortality observed in the U.S. (56%) compared with Denmark (64%), probably is explained by the early diagnosis of cancer in the U.S.

Despite the benefits of early diagnosis for preventing metastatic disease, early detection must be weighed against the unsolved issue of over-detection and over-treatment of indolent prostate cancer, researchers state in their study.

“An unwanted consequence of this earlier detection, however, is overdiagnosis and overtreatment of men harboring non-lethal localized prostate cancer whose remaining length of life would be unchanged and whose quality of life would possibly would be greater if not diagnosed at all,” Helgstrand added.