Methods
The study has received ethical approval by institutional review board of the University Hospital Motol (approval reference: EK-377/13). Data from 871 consecutive patients who underwent open or laparoscopic radical prostatectomy for clinically localized prostate cancer between May 2001 and March 2012 at our institution were reviewed. Pathological evaluation of prostate cancer surgical specimen revealed PSM in 183 patients (21.0%). Of these 183 patients, 63 (34.4%) received adjuvant treatment in terms of radiation or hormonal manipulation and these patients were excluded from the analysis. In order to provide the most accurate calculation of postoperative PSA dynamic, patients treated with neo-adjuvant hormonal and/or radiation therapy prior to the surgery were excluded from the study as well (n = 2). Additionally, since pelvic lymphadenectomy was not routinely performed in all of the patients, nodal involvement was not included in the statistical analysis and these patients (n = 2) were excluded from the study. This resulted in a final cohort of 116 patients available for statistical evaluation. Statistical comparison of clinico-pathological characteristics (PSA at diagnosis, Gleason grade, T stage) of patients with PSM excluded from the study did not differ significantly from the studied cohort (Chi-square test, Mann–Whitney test).
A positive surgical margin was defined as the presence of tumor at the inked surface of the resected specimen. Tumors were staged according to the 2002 TNM staging system. Extraprostatic extension was defined as the extension of the tumor beyond the confines of the gland into the periprostatic soft tissue. Prostate cancer Gleason grading was performed by a dedicated genitourinary pathologist. PSA determinations were carried out postoperatively on days 14, 30, 60, 90, 180 and at three monthly intervals thereafter. All the PSA tests were performed in a single hospital laboratory under standardized settings using the Immulite third-generation PSA assay (Diagnostic Products Corp, Los Angeles, California; lower detection limit 0.003 ng/ml). Biochemical recurrence was defined as a single post-nadir PSA level of 0.2 ng/ml or greater.
Statistical analysis was performed with the SAS statistical software program JMP 6 (SAS Institute, Cary, NC, USA). Mann–Whitney test and Chi-square test were used to compare several variables between groups of patients. The cut-off values of serum PSA that best predicted the biochemical progression were determined by using the Partition platform of the software. Patients were censored at the time of their last tumor-free clinical follow-up appointment. Survival analysis was performed using the Cox proportional hazard model. Pearson's correlation coefficient was used to examine the relationship between continuous variables. The receiver operating characteristic curve (ROC) and area under the curve (AUC) were determined to describe the accuracy in predicting BCR post-surgically. The significance of the difference in predictive accuracy between areas under particular ROC curves was assessed with the method of DeLong et al..[17] A P value less than or equal to 0.01 was considered statistically significant.
BMC Urol. 2014;14(79) © 2014 BioMed Central, Ltd.
