Low-molecular-weight Protein Tyrosine Phosphatase Is a Possible Biomarker for Predicting Postoperative Biochemical Recurrence in Prostate Cancer With Negative Surgical Margins

Background/Aim: For prostate cancer, positive surgical margins are considered an important predictor of biochemical recurrence. However, biochemical recurrence is observed in approximately 20% of cases, even with negative surgical margins, and some cases require salvage therapy. The elevated expression of low-molecular-weight protein tyrosine phosphatase (LMW-PTP, MW 18 kDa) is associated with a poor prognosis of certain cancers. In this study, we investigated whether the LMW-PTP expression levels could be used as a biomarker of recurrence in prostate cancer with negative surgical margins. Materials and Methods: The subjects of this retrospective study were 119 patients who underwent total prostatectomy with negative resection margins. LMW-PTP expression was categorized either as a high-expression group or as a low-expression group bye two pathologists. Subsequently, we examined the relationship between LMW-PTP expression levels and clinicopathological factors including biochemical recurrence. Results: Evaluation of the immunostained samples by two pathologists was highly reliable, with an Intraclass correlation (ICC) score for two distinct measurements of 0.77 and 0.98, respectively. Seventy-hree patients (61.3%) were placed in the LMW-PTP high expression group; and 46 patients (38.7%) were placed in the low expression group. The log-rank test revealed early biochemical recurrence in the high LMW-PTP expression group (p=0.0001). In addition, pathological T stage (p=0.004), lymphatic invasion (p=0.0456), Ki-67 labeling index (p=0.0002), and biochemical recurrence (p<0.0001) were more frequently identified in the LMW-PTP high expression group. Furthermore, multivariate analyses revealed that a high LMW-PTP expression level was an independent prognostic factor for biochemical recurrence (HR=3.14, 95% CI=1.378.07, p=0.0057). In addition, Ki-67 labeling indices were significantly higher in the high-expression group compared to the low-expression group (p<0.0001). Conclusion: LMW-PTP can be assessed using a single immunostaining protocol in a highly reproducible fashion. Tt may, thus, be applied clinically to establish the required postoperative follow-up period and determine the necessity for salvage therapy in cases of prostate cancer with negative surgical margins. LMW-PTP has the potential to be a highly useful prognostic biomarker and a therapeutic target in conjunction with other factors, such as the Gleason Score, the pathological T stage and the PSA level.