The number of new cases of metastatic prostate cancer climbed 72% in the decade from 2004 to 2013, according to a study from Northwestern University. The report considers whether a recent trend of fewer men being screened may be contributing to the rise, whether the disease has become more aggressive, or both.

However, the American Cancer Society cautioned that the Northwestern report’s “flawed analysis” did not substantiate claims that less screening could be contributing to more advanced cancers.

The Northwestern study found the largest increase in new cases was among men 55 to 69 years of age, which rose 92% in the past decade. This rise is particularly troubling, the authors said, because men in this age group are believed to benefit most from prostate cancer screening and early treatment.

In addition, the average prostate-specific antigen (PSA) of men who were diagnosed with metastatic prostate cancer in 2013 was 49, nearly double that for men diagnosed in 2004, who had an average PSA of 25, indicating a greater extent of disease at diagnosis in the more recent cases. The blood level of PSA, a protein produced by cells of the prostate gland, is often elevated in men with prostate cancer.

“One hypothesis is the disease has become more aggressive, regardless of the change in screening,” said senior author Dr. Edward Schaeffer. “The other idea is since screening guidelines have become more lax, when men do get diagnosed, it’s at a more advanced stage of disease. Probably both are true. We don’t know for sure, but this is the focus of our current work.”

The study was published in Prostate Cancer and Prostatic Diseases.

Schaeffer’s team analyzed information from the National Cancer Data Base, which included 767,550 men from 1,089 facilities nationwide who had been diagnosed with prostate cancer between 2004 and 2013. Over the past decade, there has been a substantial reduction in the number of men being screened for prostate cancer and an associated decline in the overall number of new cases of prostate cancer being reported.

“The fact that men in 2013 who presented with metastatic disease had much higher PSAs than similar men in 2004 hints that more aggressive disease is on the rise,” Schaeffer said. “If I were a patient, I would want to be vigilant. I firmly believe that PSA screening and rectal exams save lives.”

If a patient is diagnosed with localized prostate cancer that is aggressive, treatment can be curative. If men present with metastatic prostate cancer, however, treatments are not curative and only slow disease progression. Most patients with metastatic prostate cancer eventually die from the disease.

The study measured the total number of cases of metastatic prostate cancer, not the incidence. In addition, metastatic disease began rising in 2008, before the change in screening recommendations from the U.S. Preventive Services Task Force (USPSTF). Therefore, the investigators said, they can’t definitively link the increased cases to reduced screening alone.

Three percent of those included in the study had experienced metastasis by the time the cancer was diagnosed. The number of cases of metastatic prostate cancer in 2013 (2,890) was 72% greater than that in 2004 (1,685). In middle-aged men 55 to 69 years of age, the number rose 92%, from 702 new cases in 2004 to 1,345 in 2013.

“The results indicate that screening guidelines and treatment need to be refined based on individual patient risk factors and genetics,” said lead author Dr. Adam Weiner. “This may help prevent the growing occurrence of metastatic prostate cancer and potential deaths associated with the disease. This also can help minimize overdiagnosing and overtreating men with low-risk prostate cancer who do not need treatment.”

In a statement posted on one of its websites, the American Cancer Society warned against drawing too many conclusions based on the Northwestern study.

“This study makes a dramatic claim about an issue all of us have been watching eagerly: namely, whether less PSA screening might lead to more advanced cancers,” said Chief Medical Officer Otis W. Brawley, MD. “But the current analysis is far from adequate to answer that question sufficiently.” That is because the study looked at the number of metastatic disease cases rather than measuring the rates of the disease.

“A rising number of cases can be due simply to a growing and aging population among other factors,” Brawley said. “In addition, in this study, the rise they detected began before USPSTF guidelines for screening changed. There may or may not be a rise in the rates of metastatic disease, but because of a flawed analysis, this study does not answer that important question.”

Sources: Northwestern University; July 19, 2016; and American Cancer Society, July 19, 2016.