Sharing the Decision Slide Set: Slide 25

Talking Points and Text Description of Slide

Slide 25 — Harms: False Positives

Talking Points

The first type of harm is a false-positive screening test. A false-positive test means the test was positive but no cancer was found at biopsy. This table presents screening results for 100 men in the respective age categories who have never undergone screening. For our purposes, a PSA value above 4.0 is considered positive for prostate cancer.

From the slide we see that if you screen 100 men in their 50s who have never been screened, about 5 of 100 will have PSAs >4.0. Of these five, one to two will be diagnosed with prostate cancer on biopsy. Thus, a majority of men in their 50s with PSAs >4.0 will have false-positive tests.

The number of men per 100 who test positive, who have cancer, and who have false-positive screening tests increases with age. So, 10 to 12 men per 100 in their 60s and about 18 men per 100 in their 70s will have false-positive tests.

While previously screened men will likely experience fewer false-positive tests, the problem is still substantial.

Several refinements to the PSA test, such as free PSA, are being investigated. We don’t know yet if these tests reduce the number of false positives.

It should also be noted that PSA will not detect the cancers of 10% to 30% of men who have prostate cancer at the time of initial screening. These are false-negative PSA tests.

False positives are also a potential harm of screening tests for other types of cancers and other diseases.

The point to make to patients is that if we screen with PSA we will find some positive tests, most of which will not be cancer.

Sources: Labrie et al., 1999; Schroder et al., 2000; Catalona et al., 1994; Richie et al., 1993; Labrie et al., 1992; Maattahen et al., 1999; Labrie et al., 1996; Horninger et al., 2000; Martin et al., 1999; Labrie et al., 1993.

Text Description of Slide

Table shows the number of false positive tests for men in three age categories (50s, 60s, and 70s) who have never been screened for prostate cancer (100 unscreened men in each group):

• Of 100 unscreened men in their 50s, five have a PSA greater than 4, but prostate cancer is found in only 1 to 2 of them, leading to a false-positive rate of 3 to 4.



• Of 100 unscreened men in their 60s, 15 have a PSA greater than 4, but prostate cancer is found in only 3 to 5 of them, leading to a false-positive rate of 10 to 12.



• Of 100 unscreened men in their 70s, 27 have a PSA greater than 4, but prostate cancer is found in only 9 of them, leading to a false-positive rate of 18.