Millions of Americans may have heard on the news last week that metastatic prostate cancer was increasing dramatically in the United States. However, national data demonstrate that, in fact, the rates are not changing. Using data collected by cancer registries across the United States, the North American Association of Central Cancer Registries (NAACCR, Inc.) found that rates of metastatic prostate cancer rates are stable.
In a newly released study, “Increasing incidence of metastatic prostate cancer in the United States (2004–2013)” which was e-published in the journal Prostate Cancer and Prostatic Diseases on July 19, 2016, the authors present findings inconsistent with other studies of prostate cancer trends. Prostate cancer incidence and mortality have been declining for many years, and recent rates of metastatic disease are stable, not increasing as the authors’ state in their paper.
The reason for the discrepancy between this study and other published literature is that the wrong measure was used for incidence. The authors equated a change in the count of metastatic prostate cancer to an increase in risk of metastatic prostate cancer. But counts of cases do not answer public health questions about risk and using counts can result in misleading conclusions. To compare risk of prostate cancer in two populations or the same population over time, we must use age-adjusted incidence rates.
Figure 1, using NAACCR’s Cancer in North America (CiNA), a population-based dataset covering 97% of United States population including data from the Centers for Disease Control and Prevention (CDC) National Program of Cancer Registries (NPCR) and National Cancer Institute (NCI) Surveillance, Epidemiology and End Results (SEER), shows that metastatic prostate cancer incidence rates, the true measure of risk, were virtually unchanged between 2004 and 2013. Use of PSA for prostate cancer screening is now no longer recommended and fewer men are electing to be screened by PSA. Consequently, fewer asymptomatic, local stage cases are being diagnosed, as seen in the top line of the graph.
We also note that the data set used by the authors was not population-based and represents a subset of the total cases of prostate cancer in the US. The authors used the National Cancer Data Base (NCDB), which is not a population-based sample but a subset of the US cancer cases collected from American College of Surgeons (ACoS) approved hospitals. An estimated 30-40% of the total cancer cases in the US are diagnosed in non-ACoS approved facilities. ACoS approved hospitals tend to be large facilities located in urban settings and their patients may have distinct differences from the population at risk of developing prostate cancer.
It is not unusual for researchers to have differing interpretations of the same data. But it is imperative that proper epidemiologic measures are used in public health research. NAACCR, along with its partners the American Cancer Society (ACS), CDC, and NCI are working together to clarify the issues raised by this methodology further delineating our concerns about the authors’ representation and interpretation of these data.
Increasing incidence of metastatic prostate cancer in the United States (2004-2013) (The linked report was published on PubMed)
Changes in prostate cancer screening practices in the United States have led to recent declines in overall incidence, but it is unknown whether relaxed screening has led to changes in the incidence of advanced and metastatic prostate cancer at diagnosis.
We identified all men diagnosed with prostate cancer in the National Cancer Data Base (2004-2013) at 1089 different health-care facilities in the United States. Joinpoint regressions were used to model annual percentage changes (APCs) in the incidence of prostate cancer based on stage relative to that of 2004.
The annual incidence of metastatic prostate cancer increased from 2007 to 2013 (Joinpoint regression: APC: 7.1%, P<0.05) and in 2013 was 72% more than that of 2004. The incidence of low-risk prostate cancer decreased from years 2007 to 2013 (APC: -9.3%, P<0.05) to 37% less than that of 2004. The greatest increase in metastatic prostate cancer was seen in men aged 55-69 years (92% increase from 2004 to 2013).
Beginning in 2007, the incidence of metastatic prostate cancer has increased especially among men in the age group thought most likely to benefit from definitive treatment for prostate cancer. These data highlight the continued need for nationwide refinements in prostate cancer screening and treatment.Prostate Cancer and Prostatic Diseases advance online publication, 19 July 2016; doi:10.1038/pcan.2016.30.
The opinions expressed in this article are those of the authors and may not represent the official positions of NAACCR.