High PSA levels could indicate prostate cancer. (CBC)

Men with a brother who has prostate cancer are more likely than other men to be diagnosed with the disease, but screening rather than genetics may be behind it, a new study suggests.

When Swedish researchers looked at data from 22,511 brothers of 13,975 prostate cancer patients, they found the incidence of the cancer was higher among brothers than men of the same age.

But the type of cancer most often detected was early-stage prostate cancer usually identified with a prostate specific antigen or PSA test that may or may not be dangerous, Dr. Ola Bratt of the urology department at the Helsingborg Hospital in Sweden and colleagues said in Thursday's online issue the Journal of the National Cancer Institute.

Brothers of prostate cancer patients were at 3.1 times increased risk for a diagnosis of prostate cancer, the researchers found. Most of the tumours diagnosed were low-grade ones that likely would never be found and never produce symptoms.

"The increased diagnostic activity among men with a family history of prostate cancer, which we observed, will inflate family history as a risk factor for prostate cancer in populations of men who commonly receive PSA testing," the study's authors concluded.

The risk of diagnosis was 4.3 times as high in the first year after a family member had been diagnosed, which points to the role of screening.

The risk also was higher for men of higher socioeconomic status, who were more likely to seek testing.

In an accompanying editorial, Dr. Ian M. Thompson of the University of Texas and colleagues suggested doctors change their approach of seeking risk factors for prostate cancer to assessing factors related to "biologically consequential prostate cancer" such as metastatic disease.

Some prostate tumours are harmless while others are aggressive and could become life threatening, but there currently is no easy way to tell the difference.

The study was funded by the Swedish Research Council project, Swedish Cancer Society and Vasterbotten County Council.