Prostate Imaging Not Recommended for Men with Low PSA Levels

After definitive prostate cancer therapy, there is little value in imaging studies when patients with biochemical failure are asymptomatic and have prostate-specific assay (PSA) levels less than 5 ng/ml, according to researchers.

This conclusion, reported by a Cleveland Clinic (Cleveland, OH, USA; www.clevelandclinic.org) team of investigators at a prostate cancer symposium at American Society of Clinical Oncology (ASCO) held in Kissimmee (FL, USA) in late February 2007, emerged from data gathered from the Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE), a 13,000-patient database. The CaPSURE database is a U.S. observational registry with longitudinal data on men with biopsy-proven disease.

There was a ninefold increase in the likelihood of negative findings on imaging studies for patients with PSA levels below 5 ng/ml compared with patients whose biochemical failure was indicated by PSA levels 5 ng/ml or higher, said Toni Choueiri, M.D., a hematology and medical oncology fellow in Cleveland.

According to Dr. Choueiri, imaging studies are typically ordered to identify distant metastases and guide treatment. However, this analysis suggests that many times those studies are unnecessary. Dr. Choueiri and colleagues identified 292 patients in the database who had biochemical failure and had subsequent imaging studies performed with bone scans, computed tomography (CT), or magnetic resonance imaging (MRI). Only 31 (11%) of those imaging studies were positive. In addition to the PSA threshold, Dr. Choueiri reported that the data also suggest that PSA doubling time should be factored into the decision to order imaging studies.

In the study, patients with a PSA doubling time greater than 10 months had more than a fourfold increase in negative imaging studies compared with patients who had a PSA doubling time of less than 10 months. Biochemical failure was defined as three consecutive PSA rises above the nadir for radiation therapy patients and as two consecutive PSA of at least 0.2 ng/m for radical prostatectomy patients.

The median trigger PSA (the PSA test that prompted clinicians to order imaging studies) was 1.2 ng/ml, according to Dr. Choueiri. He concluded that in the absence of disease-related symptoms, "imaging studies are unlikely to identify distant metastases when trigger prostate-specific antigen is less than or equal to 5 ng/ml and PSA doubling time is greater than 10 months.”




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