MATERIALS AND METHODS
Data of patients who underwent RP as the initial treatment of PCa were
reviewed retrospectively in this study. The data source was nationwide
PCa database of Turkish Urooncological Association. A total of 3646
patients were found to be treated with RP for localized disease in the
database and excluding patients with missing data, study population was
downsized to 2454 patients. Patients were divided into two groups
according to their waiting period between diagnosis and RP. The waiting
period in respective groups was; Group 1: less than or equal to 3
months, Group 2: more than 3 months.
Based on D’amico classification system patients were stratified into
low, intermediate and high-risk groups. The date of prostate biopsy was
regarded as the diagnosis date and time to treatment is calculated as
the number of days between the date of RP and the diagnosis date.
Patients who received treatment for PCa (radiotherapy or androgen
deprivation therapy etc.) prior to RP or patients who were first
enrolled on AS protocol were excluded from the study.
All patients were diagnosed with either standard transrectal ultrasound
guided biopsy or magnetic resonance (MR) guided fusion biopsy. All RPs
were included in the study irrespective of the surgical approach (robot
assisted, laparoscopic or open). Patients were operated by a senior
urology staff in each participating center. Both biopsy and RP specimens
were evaluated by a dedicated uro-pathologist in each center.
Biochemical recurrence which was defined as a prostate specific antigen
(PSA) value measured greater than 0.2 ng/ml during the follow up after
RP, is designated as the primary endpoint for this study. Secondary
endpoints of the study were surgical parameters, pathological upgrading,
metastasis on follow up and the need for additional treatments. For
time-based analysis and comparison of oncological outcomes (biochemical
recurrence free survival, need for adjuvant treatment or metastasis free
survival), only patients with a follow up duration of more than 1 month
was included in the statistical tests.
The study data were collected by REDCap data collection software
developed by Vanderbilt University and licensed to Turkish Urooncology
Association. 5, 6 All data are kept in a secure server
and all personal information of patients were anonymized.
For statistical analysis Python Programming Language (Open source v3.7)
was used with the help of pandas, matplotlib, numpy, scipy and lifelines7 libraries. JupyterLab (Open source v1.2.6) was used
as the coding interface. The scalar variables were analyzed using visual
(histograms, probability plots) and analytical methods
(Kolmogorov-Simirnov/Shapiro-Wilk’s tests) to determine whether or not
they were normally distributed. Descriptive analyses were given as means
and standard deviations when the variable was normally distributed.
Medians and interquartile ranges were used if the variable was not
normally distributed. For the comparison of scalar variables between two
groups, t-test or Mann-Whitney U test were used for normally and
non-normally distributed variables respectively.
Categorical variables were compared with Chi-square test between groups.
If the assumptions of Chi-square do not hold due to low expected cell
counts Fisher’s exact test were used for the comparison of categorical
variables. For biochemical recurrence free survival variable,
Kaplan-Meier survival estimates were calculated. A separate log rank
test was used to estimate independent effect of waiting duration group
on time to biochemical recurrence. The possible factors identified in
univariate analysis further evaluated with Cox regression. The
proportional hazard assumption was assessed by means of residual
analysis. For all statistical tests, p value below 0.05 was considered
statistically significant.