Plasma Levels of Heat Shock Protein 70 in Patients with Prostate Cancer: A Potential Biomarker for Prostate Cancer

Heat shock protein 70 (Hsp70) is a stress-inducible protein that is also known for its inhibitory effects on apoptosis. Increased Hsp70 expression is reported in a variety of tumor tissues. Heat shock protein 70 is detectable in plasma and could potentially be used as a biomarker for diagnosis or disease stratification. The relationship between plasma levels of Hsp70 and prostate cancer status has not been well studied. Our study was designed to test this relationship. One hundred twenty-five patients with localized/untreated or hormone-refractory prostate cancer were identified. Forty-five healthy male blood donors between 50 and 73 years of age served as controls. EDTA plasma was subjected to quantitative sandwich immunoassays for both Hsp70 and prostate-specific antigen (PSA). Wilcoxon rank-sum tests were used to examine differences by category. Maximally selected χ² statistics were used to identify cutoff points to best distinguish between categories. Plasma Hsp70 levels in the patients with localized untreated disease (n = 68; median, 0.8 ng/mL; interquartile range, 0.5-2.0) were significantly higher than those in the control group (n = 45; median, 0.5 ng/mL; interquartile range, 0.3-0.8; P = 0.0037). Although the primary cutoff point (1.15 ng/mL) significantly distinguished the localized untreated patients from the control group, plasma Hsp70 levels did not prove more effective than PSA as a predictor for diagnosis or stratification of patients with prostate cancer in the context of group comparisons. Nonetheless, several patients in the localized untreated group showed higher plasma levels of Hsp70 than the primary cutoff point even though their PSA levels were within normal range (< 4 ng/mL). Heat shock protein 70 is a marker of prostate cancer, although its clinical utility is uncertain. It is possible that when used in conjunction with PSA it might prove useful in identifying patients with early-stage prostate cancer who might otherwise be missed by PSA screening alone.