Background: Thymidine Kinase 1 (TK1) is a cytosolic enzyme that plays an important role in DNA precursor synthesis and TK1 enzyme activity in serum is an established biomarker for prognosis and treatment monitoring, particularly for haematological malignancies. The AroCell TK 210 ELISA determines TK1 protein levels, in contrast to TK1 activity, and it has demonstrated superior sensitivity in distinguishing between subjects with solid tumours and controls.

Pro PSA, free PSA and the prostate health index (PHI) have been proposed as more discriminating tests than PSA in distinguishing between benign and cancerous prostate changes. The purpose of this study was to compare the AroCell TK 210 ELISA with PSA, free PSA, pro PSA and PHI in men with pre-cancerous conditions, and patients with confirmed prostate cancer.

Experimental Procedures: Serum samples from 94 patients with known PSA values (in the range 2 to 10 µg/L) that were under investigation for prostate cancer were collected at the University Medical Centre, Ljubljana. TK1 protein levels were determined using the AroCell TK 210 ELISA. PSA, fPSA and pro PSA levels were analysed with commercial assays (Hybritech PSA, Hybritech Free PSA and Access 2pPSA - Beckman Coulter USA) analysed on the Access 2 Beckman Coulter analyzer.

Results: Overall, 16/94 patients had serum TK1 protein levels above the estimated cut-off value for age-matched healthy men (0.45µg/L). 65/94 men had pre-cancerous prostate conditions, including benign prostate hyperplasia, prostatitis and high grade prostatic intraepithelial neoplasia, while 29 patients had confirmed prostate cancer (PCa). Only 7 /65 in the pre-cancerous group (11%) had TK1 protein levels above the cut-off, whereas in the prostate cancer group 9 out of 29 (31%) were positive. Moreover, the TK1 protein values in the PCa group (mean=0.41µg/L) differed significantly from those with pre-cancerous conditions (mean=0.31µg/L, P=0.01). Further analysis showed that pro PSA and PHI also differentiated the prostate cancer group from those with pre-cancerous conditions (P= 0.01 and P<0.001, respectively). This was not observed for fPSA and PSA. Overall, the AroCell TK 210 ELISA showed significant correlation with PHI (r=0.32, P=0.0017) and pro PSA (r=0.21 P=0.044) but not with fPSA or PSA.

Conclusions: This preliminary study has demonstrated that serum TK1 assayed with the AroCell TK 210 ELISA can differentiate between pre-cancerous and prostate cancer patients with a similar accuracy to that of pro PSA. Further clinical studies will establish the capacity of the AroCell TK 210 ELISA to complement pro PSA and PHI in distinguishing between pre-cancerous and prostate cancer, potentially providing another tool in prostate cancer management.

Citation Format: Jagarlamudi Kiran Kumar, Staffan Eriksson, Zupan Moca, Kumer Kristina, Josko Osredkar, Fabjan Teja, Hlebic Gregor, T Smrkolj. The AroCell TK 210 ELISA may complement Pro PSA and the Prostate Health Index in differentiating pre cancerous and cancerous conditions in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 715. doi:10.1158/1538-7445.AM2017-715