Usefulness of alpha₁-antichymotrypsin-PSA complex for predicting bone metastases of prostate cancer

Objectives: To determine the usefulness of alpha₁-antichymotrypsin-prostate-specific antigen (PSA) complex (PSA-ACT)-based parameters in predicting bone metastasis in patients with prostate cancer. Methods: PSA-ACT, total PSA, free PSA, their volume-adjusted values, and alkaline phosphatase were evaluated in 220 consecutive patients with newly diagnosed prostate cancer. Results: Bone metastases were detected by bone scan in 27 (12.3%) of the 220 patients. The serum levels of PSA-ACT, total PSA, free PSA, PSA density, PSA adjusted for transition zone volume, PSA-ACT density, PSA-ACT adjusted for transition zone volume, alkaline phosphatase, PSA-ACT/PSA ratio, and Gleason score in patients with bone metastases were each significantly greater than in those without bone metastases. On receiver operating characteristic analyses, PSA-ACT had the greatest area under the curve (0.88), but the receiver operating characteristic curve demonstrated that the sensitivity and specificity of PSA-ACT were marginally better than those of total PSA at only a few selected cutoff points. At a sensitivity of 93% (2 patients with bone metastasis missed), unnecessary bone scans would have been avoided in 107 and 102 patients using a PSA-ACT cutoff value of 10 ng/mL and total PSA cutoff value of 11.5 ng/mL, respectively. Multivariate logistic regression analysis demonstrated that PSA-ACT and Gleason score were significant independent predictors of bone metastasis. Conclusions: PSA-ACT is as useful as total PSA for identifying patients with a low probability of having bone metastasis. PSA-ACT could replace PSA for predicting negative bone scans in a clinical setting in which PSA-ACT is used for monitoring and screening patients for prostate cancer.