Prostate Cancer Screening: Biopsy Techniques Have Made PSA Test Less Predictive

ScienceDaily (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. 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 ?Y2.0 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.

Advantages And Drawbacks

PSA is measured by nanograms per milliliter of blood, with most healthy men having under 4 ng/mL. According to the American Cancer Society, a PSA level between 4 and 10 indicates a 25% chance of it being prostate cancer. A PSA higher than 10 means there’s at least a 50% chance its prostate cancer.

Here are some advantages and drawbacks to the PSA test that men should be aware of.

Benefits of the PSA Test

* Prostate cancer can be detected by the test long before symptoms present themselves.

* The test detects cancer 5 to 10 years earlier than digital rectal exams (DREs).

* Early detection before the cancer has spread outside the prostate provides men with more treatment options and a better chance for a cure.

* Though this is a controversial claim by some experts, the test may contribute to significant reduction deaths from prostate cancer.

* The test is a quick, simple and painless procedure involving a medical staffer taking a sample of blood for testing in a lab.

Drawbacks of the PSA Test

* Significant number of false negatives. In 1 out of 5 cases, the PSA test comes back 'normal' with PSA levels in men with early prostate cancer.

* High rate of false-positive results. Two out of 3 of those with elevated levels of PSA do not have prostate cancer, so the test may cause undue worry.

* A false-positive result can lead to unnecessary follow-up testing that is more invasive, i.e., multiple biopsies.

* The test does not distinguish between prostate cancer and other prostate problems such as infection and BPH – again, leading to more false positives and unnecessary follow-up procedures.

* Men over the age of 75 may not benefit from the test because the prostate is generally very slow growing and treatment is unlikely to lengthen their lives.

Read more at Suite101: PSA Test for Prostate Cancer: Advantages And Drawbacks | Suite101.com http://cancer.suite101.com/article.cfm/psa_test_for_prostate_cancer#ixzz0a0oIuwOM

For whom might a PSA screening test be recommended?

Doctors’ recommendations for screening vary. Some encourage yearly screening for men over age 50, and some advise men who are at a higher risk for prostate cancer to begin screening at age 40 or 45. Others caution against routine screening. Although specific recommendations regarding PSA screening vary, there is general agreement that men should be informed about the potential risks and benefits of PSA screening before being tested. Currently, Medicare provides coverage for an annual PSA test for all men age 50 and older.

Several risk factors increase a man’s chances of developing prostate cancer. These factors may be taken into consideration when a doctor recommends screening. Age is the most common risk factor, with nearly 63 percent of prostate cancer cases occurring in men age 65 and older (1). Other risk factors for prostate cancer include family history, race, and possibly diet. Men who have a father or brother with prostate cancer have a greater chance of developing prostate cancer. African American men have the highest rate of prostate cancer, while Asian and Native American men have the lowest rates. In addition, there is some evidence that a diet higher in fat, especially animal fat, may increase the risk of prostate cancer.