## 4 Discussion  
The present study found that preoperative parameters including initial PSA, biopsy GS, greatest percentage of biopsy core, number of positive biopsy cores, MRI finding of PIRADS score, probability of ECE, and postoperative pathologic parameters including tumor volume, PSM, LVI, and PNI were significantly associated with early BCR. Utilizing not only all these variables but also preoperative clinical and imaging variables, the prediction algorithm based on an auto-encoder showed a higher prediction ability of early BCR after RP than those of other algorithms, with an AUC of 0.638 with all parameters, and 0.656 with preoperative parameters. Prior studies suggested several prediction models using various combinations of variables including initial PSA, greatest percentage of biopsy cores, number of positive biopsy cores, GS, and cancer stage for successful risk stratification, as well as oncologic outcomes including metastatic progression and prostate cancer-specific mortality following treatment [1; 16; 17; 18; 19; 20; 21; 22]. In our study, variables related to early BCR were in accordance with those in prior studies. We defined early BCR as postoperative PSA levels greater than 0.2 ng/ml occurring on two separate occasions, or patients who had to undergo salvage therapy at their one-year follow-up. Notably, BCR does not necessarily result in clinical recurrence or cancer-specific mortality due to the indolent nature of prostate cancer and the remaining benign prostatic tissue after RP [14]. Nevertheless, several groups have investigated prognostic factors among men with BCR after RP and revealed that the time to BCR was one of the predictors of prostate cancer-related mortality [20; 23]. Prior studies demonstrated the importance of information obtained from the time of diagnosis [17; 19; 21]. They focused on the PSA level at the time of diagnosis and biopsy results. In our study, an auto-encoder-based prediction model using only the preoperative parameters as input data shows moderate diagnostic performance, even higher than when all parameters are used as input data. The Gleason grading system consistently shows the prognostic impact in patients with prostate cancer [24]. In particular, we identified that the higher the biopsy Gleason grading, the more often the early BCR occurred, albeit not surgical Gleason grading. Several studies have investigated the association between initial biopsy  
Figure 3: ROC curve using preoperative parameters: (**a**) Multi-layer perceptron, (**b**) decision tree, (**c**) KNN, and (**d**) auto-encoder. characteristics and postoperative pathological features or oncologic outcomes. However, results from various series have been mixed and inconsistent [25; 26; 27]. This may be due to operator dependency, although a transracial ultrasound-guided prostate biopsy is the standard procedure for diagnosing prostate cancer and is a well-established standard method [28]. Nevertheless, the higher the greatest percentage of biopsy cores or number of positive cores, the more frequently early BCR occurred in our population. Interestingly, while SVI, and ECE, representing pathologic T staging, were not different between early BCR and non-BCR patients, the proportion of definite or probable findings of SVI and ECE on MRI was significantly higher in early BCR patients (13/20 vs. 19/84; \(p<0.001\)). Moreover, PIRADS scores differed between groups. Only one patient with PIRADS \(\leq\) 3 showed early BCR after RP. The PI-RADS released in 2012 by the European Society of Urogenital Radiology [29], updated to v2 in 2015, and updated to v2.1 in 2019 [30; 31], has become a standardized tool for the early detection of clinically significant prostate cancer in patients with good diagnostic performance. Reportedly, both diffusion restriction and enhancement patterns could reflect tumor aggressiveness in prostate cancer; the lower the ADC or the earlier the enhancement was observed, the more aggressive tumors were found pathologically [32; 33].