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Comparison of Free and Total Forms of Serum Human Kallikrein 2 and Prostate-Specific Antigen for Prediction of Locally Advanced and Recurrent Prostate Cancer

Departments of¹ Surgery (Urology), ² Epidemiology and Biostatistics, ³ Clinical Laboratories, and ⁴ Medicine (GU-Oncology), Memorial Sloan-Kettering Cancer Center, New York, NY.
⁵ Department of Urology, University Hospital Hamburg-Eppendorf, Hamburg, Germany.
⁶ Department of Biotechnology, University of Turku, Turku, Finland.
⁷ Department of Laboratory Medicine, Division of Clinical Chemistry, Lund University, University Hospital, Malmö, Sweden.

^aAddress correspondence to this author at: Memorial Sloan-Kettering Cancer Center, Departments of Clinical Laboratories, Urology, 1275 York Ave., Box 213, New York, NY 10021. Fax 212-422-2379; e-mail liljah{at}mskcc.org.

Background: We evaluated the association of total and free forms of serum human kallikrein 2 (hK2) and prostate-specific antigen (PSA) with prostate cancers of unfavorable prognosis.

Methods: We retrospectively measured total PSA (tPSA), free PSA (fPSA), and total hK2 (thK2) in preoperative serum samples from 867 men [and assessed free hK2 (fhK2) measured in 577 of these men] treated with radical prostatectomy for clinically localized prostate cancer. Associations between biomarker concentrations and extracapsular extension, seminal vesicle invasion, and biochemical recurrence (BCR) were evaluated. A subset of patients with PSA 10 µg/L, the group most commonly seen in clinical practice in the US, was analyzed.

Results: thK2 was the strongest predictor of extracapsular extension and seminal vesicle invasion (areas under the ROC curve [AUC], 0.662 and 0.719, respectively), followed by tPSA (AUC, 0.654 and 0.663). All biomarkers were significant predictors of BCR. hK2 forms, but not PSA forms, remained highly significant for predicting BCR in the low-PSA group. Combining tPSA, fPSA, and thK2 in a multivariable model improved prediction compared with any biomarker used individually (AUC, 0.711, 0.755, and 0.752 for this combination predicting extracapsular extension, seminal vesicle invasion, and BCR, respectively; P <0.001 for all).

Conclusions: Increased concentrations of hK2 in the blood are significantly associated with unfavorable features of prostate cancer, and thK2 is predictive of locally advanced and recurrent cancer in patients with PSA 10 µg/L. Independent of tPSA and fPSA, hK2 predicts unfavorable prognosis.