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Phil Gunby

JAMA. 1999;281:2274-2275.

	Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.

Dallas—As some clinicians consider lowering the prostate-specific antigen (PSA)–alerting threshold for possible adenocarcinoma to 2.5 ng/mL, researchers are exploring a role for an enzymatic "cousin" of PSA in this diagnostic process.

This substance is human kallikrein 2 (hK2) enzyme, recently purified by Donald J. Tindall, PhD, at the Mayo Clinic Foundation in Rochester, Minn. The enzyme has an 80% structural similarity to PSA, which technically is hK3. Like PSA, hK2 is secreted by prostate epithelial cells, and normally converts the inactive form of PSA (pro-PSA) into the enzymatically active form (PSA, the enzyme). (The other known human kallikrein enzyme, hK1, is not produced by the prostate.)

THE "FREE PSA" TEST

A current "free PSA" blood test for prostate cancer measures the unbound (the numerator) to total PSA (the denominator) ratio. It works this way: When prostate cells turn cancerous, the PSA they produce tends to leak into . . . [Full Text of this Article]