Biopsy techniques have made PSA test less predictive

Mar 11 2008

Prostate specific antigen (PSA) levels typically have correlated with prostate biopsy results in the detection of prostate cancer, but that correlation no longer exists for men with a normal prostate exam, according to a new study published in the April 15, 2008 issue of CANCER, a peer-reviewed journal of the American Cancer Society.

The study suggests that improved biopsy techniques make PSA less useful in prostate cancer screening.

PSA tests have been lauded as important diagnostic tools for prostate cancer, however much of the data used to make this conclusion were generated in the early to mid 1990s, when prostate biopsies were performed differently than they are today. Since that time, there has been an increase in the number of prostate biopsies performed and an increasing number of biopsy samples taken from each patient.

Douglas Scherr, MD, Michael Schwartz, MD, and colleagues at the New York Presbyterian Hospital of the Weill Medical College of Cornell University, in New York City, set out to assess whether changes in prostate biopsy practices might have changed the predictive value of PSA tests.

The researchers performed a retrospective analysis of all prostate biopsies performed at their institution between 1993 and 2005, finding 1,607 that satisfied their inclusion and exclusion criteria. Douglas Scherr, MD and his team divided patients into three groups based on when they received their biopsies: 1993-1997, 1998-2001, and 2002-2005. They examined each group for the number of biopsies performed, the number of positive biopsies, patient age, most recent PSA prior to biopsy, prostate volume, and number of biopsy samples taken. With these data in hand, they assessed potential correlations between PSA levels and positive biopsy rate.

The investigators found that the number of biopsies performed, the percentage of positive biopsies, and patient ages did not change significantly over time. However, there was a significant decrease in the median PSA level in patients undergoing biopsy and an increase in the median number of samples taken at the time of biopsy. Also, fewer biopsies were performed for the indication of a suspicious digital rectal exam and there was an increase in the percentage of patients undergoing biopsy for PSA readings between 2.5 and 3.99 ng/ml. (According to the American Cancer Society, the PSA level usually goes above 4 ng/ml when prostate cancer develops, but about 15% of men with a PSA below 4 ng/ml will have prostate cancer on biopsy.)

The positive biopsy rate in men with PSA levels in the 2.0 to 3.99 ng/ml range equaled or surpassed that for patients with higher PSA readings. Therefore, the researchers concluded that ¡°the correlation between PSA and positive biopsy rate no longer holds true in our patient population for men with a normal digital rectal exam and PSA ¡Ý2.0 ng/ml.¡±

While changes in biopsy practice patterns have improved cancer detection, these very changes ¡°have negatively influenced the predictive value of PSA in men with a normal digital rectal exam such that, using current biopsy practice patterns, PSA no longer correlates with positive biopsy rate,¡± note the authors. They cite the urgent need for new blood or urinary markers to better determine who needs a prostate biopsy, adding that aside from family history or prior atypical biopsy findings, there is little other information available to help physicians decide who needs a biopsy and who does not.