Abstract 2012: Accurate measurement of free and complexed PSA concentrations in serum of women using a novel technology with fg/mL sensitivity

Abstract

Abstract Measurement of free and complexed PSA (prostate specific antigen; complexed with ACT) in certain patient groups such as prostatectomy patients and women at risk of breast and ovarian cancer has been limited by the sensitivity of current immunoassay technology (5-30 pg/mL for common clinical analyzers). Fifth generation assays for total PSA with detection limits of 0.05 to 0.1 pg/mL have been described (McDermet 2009; Thaxton 2009; Wilson 2011). We developed a next-generation assay format based on MSD's MULTI-ARRAY® electrochemiluminescence technology with detection limits of 2 fg/mL (0.002 pg/mL) for complexed PSA (cPSA) and 20 fg/mL for free PSA (fPSA), requiring only 25 μL of serum or plasma per measurement. Assays were calibrated against the WHO standards 96/668 (free PSA) and 98/670 (90% complexed, 10% free PSA). The dynamic range of both assays was three to four orders of magnitude. Typical intra-plate coefficients of variation ranged from 5% to 15%. LLOQ's of cPSA and fPSA assays were 5 fg/mL and 55 fg/mL, respectively. Spike recovery and dilution linearity were between 80% and 120%. Approximately 100 serum samples from women were evaluated. Free PSA was detectable in 95% of samples and cPSA was detectable in all samples. Multiple literature reports indicate that free PSA might be a marker for early detection of breast cancer; however, the concentrations of many samples were close to or below the detection limits of the assays used for the studies. We tested 48 serum samples from patients with breast cancer and 37 serum samples from apparently healthy women. As the table below shows, there was no clear difference between PSA concentrations in cases and controls. Free PSA [fg/mL] (Median, IQR)cPSA [fg/mL] (Median, IQR)Free/cPSA (Median, IQR)Apparently Healthy (n = 37)150 (80-260)560 (210-1,500)0.29 (0.18-0.73)Breast Cancer (n = 48)90 (50-260)180 (90-480)0.36 (0.17-0.77)Breast Cancer, ER positive (n = 10)160 (80-660)170 (120-13,000)0.62 (0.22-1.8)Breast Cancer, HER2 positive (n = 10)160 (50-290)460 (110-8,300)0.10 (0.03-0.44)Breast Cancer, triple negative (n = 10)90 (40-370)140 (50-300)0.68 (0.34-1.9) In conclusion, we developed a next-generation assay format that is 100 to 1000 times more sensitive than the currently available clinical PSA assays. This enables accurate determination of free PSA and cPSA concentrations in the serum of females. Citation Format: Galina N. Nikolenko, Martin K. Stengelin, Laukik Sardesai, Eli N. Glezer, Jacob N. Wohlstadter. Accurate measurement of free and complexed PSA concentrations in serum of women using a novel technology with fg/mL sensitivity. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2012. doi:10.1158/1538-7445.AM2015-2012