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Pathology · Neoplasia: PSA in prostate cancer
Sample itemA 66-year-old man has a total PSA of 7.5 ng/mL and a normal digital rectal examination. The free-to-total PSA ratio is 8%. How should this be interpreted?
Original practice item, not a recalled exam question. Nothing here is recorded.
The answer and the reasoning
A. A low ratio raises the likelihood of prostate cancer, so a biopsy should be considered
PSA is organ-specific but not cancer-specific, and it is raised in benign hyperplasia, prostatitis and after instrumentation. In cancer, more PSA is bound to alpha-1-antichymotrypsin, so the free fraction is low. A free-to-total ratio below about 10% in the 4 to 10 ng/mL range raises concern, whereas a high ratio favours benign disease.
Option by option
A. A low ratio raises the likelihood of prostate cancer, so a biopsy should be considered (correct)
A low free fraction indicates more complexed PSA, as seen in cancer, and supports biopsy.
B. A low ratio favours benign prostatic hyperplasia, so no further work-up is needed
Benign hyperplasia is associated with a higher free fraction, so a low ratio does not reassure.
C. The ratio is irrelevant because PSA is specific for cancer at this level
PSA is not cancer-specific, and the ratio helps to refine risk in the borderline range.
D. A ratio above 25% would favour cancer, so this result excludes it
The relationship is the reverse: a high free fraction favours benign disease.
Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.
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