## 1 Introduction  
Prostate cancer is the most commonly diagnosed cancer in men worldwide, the most frequently diagnosed cancer in 112 countries, and the second-ranked cause of mortality following lung cancer [1]. Treatment options for prostate cancer vary according to the tumor stage and grade, patient characteristics, and personal preferences. Previously, some guidelines were published based on the current evidence in prostate cancer diagnostics, such as the National Comprehensive Cancer Network (NCCN) guidelines and the European Association of Urology-European Society for Radiotherapy and Oncology-International Society of Geriatric Oncology guidelines [2,3]. According to the NCCN guidelines, prostate cancer has been categorized into six risk groups, from very low to very high, based on prostate-specific antigen (PSA), Gleason score (GS), and TNM classification [2]. PSA is a continuous parameter of prostate cancer. In the prostate cancer grading system, the biopsy GS consists of the Gleason grade of the most extensive pattern plus the highest pattern. In the 2014 International Society of Urological Pathology, prostate cancer was classified into five levels according to the GS, which highlighted the clinical differences between GS 7 = 3 + 4 and GS 7 = 4 + 3 [4]. For the staging of prostate cancer, the use of the 2017 TNM classification of the American Joint Committee on Cancer was recommended. Initial therapies, such as active surveillance, radiation therapy, radical prostatectomy, and androgen deprivation therapy, were selected based on the risk groups and expected patient survival. Thus, the risk classification of prostate cancer is important. A prostate cancer diagnosis is made in three steps. The latest prostate cancer screening and clinical practice guidelines highly recommend PSA screening as the first step in the algorithm classifying prostate cancer risk based on the European Randomized Study of Screening for Prostate Cancer results [3; 5; 6; 7]. The Japanese Urological Association guidelines provide a PSA cut-off value of 4.0 ng/mL for further urological examination, with an age-standardized PSA cut-off value of 3.0, 3.5, and 4.0 ng/mL for men aged 50-64, 65-69, and \(\geq\)70 years, respectively [6]. The second step in establishing a definitive diagnosis is a prostate biopsy, with the option of two invasive approaches that have similar detection rates. One is the transrectal or transperineal ultrasound-guided biopsy, and the other is the transrectal biopsy. A transperineal approach requires anesthesia, while the transrectal approach has a higher severe infection risk [8]. Current guidelines recommend performing multiparametric magnetic resonance imaging (MRI) before biopsies to discriminate patients with prostate cancer as indolent or clinically significant. The GS is the most commonly used histopathological grading system, based on the classification of five histological patterns underlying the presence of cancer cells in the specimen. The grade group was determined according to the GS [9]. Staging was performed according to the TNM classification system published by the Union for International Cancer Control. Multiparametric MRIs, comprising T2-weighted imaging (T2 WI), dynamic contrast-enhanced imaging, and diffusion-weighted imaging (DWI), are highly reliable and were used for tumor (T) staging. Current multiparametric MRI diagnostic methods follow the Prostate Imaging Reporting and Data System (PI-RADS), which involves a semiquantitative radiologist assessment of each suspicious lesion, assigning a corresponding clinically significant prostate cancer likelihood score from one to five [10]. PI-RADS scores with other parameters, such as clinical variables, family history, or PSA levels, help radiologists determine whether further investigation is needed to make a final diagnosis. For N staging, abdominal computed tomography (CT) and MRI indirectly assess nodal invasion by using lymph node diameter and morphology.