3D printing technology, an emerging technology, is based on computer graphic data overlaying specific materials to create any shape of products. One of the most common printing methods is Fused Deposition Modeling (FDM)-that is, FDM builds structures by depositing material, like plastic, acrylonitrile butadiene styrene, polylactic acid, layer by layer (1). The technology bridges the gap between two-dimensional (2D) imaging and realistic anatomy, providing a more tangible method for the evaluation and comprehension of pathology (2). Thus, it has the potential to be increasingly important inpatient counseling (3), and in the training of residents and students (4, 5), as well as in surgical decision making and planning for complicated conditions and procedures (6).

This review aims to give an overview of the role of 3D-printed models currently used in urologic cancer, especially in renal cancer, bladder cancer, prostate cancer, and to explore future directions of research in this field.

A systematic search was conducted in the electronic databases PubMed and Embase, and all relevant articles were published in English from their starting dates to June 2021 (Table 1). The search strategy used the following keywords relating to the 3D physical model printing (e.g., three-dimensional printing, 3D printing, 3D printed, 3D physical reconstruction, 3D model) in combination with urologic cancer (e.g. adrenal cancer, kidney cancer, urethral tumor, bladder cancer, prostate cancer, testicular cancer). All identified abstracts were carefully reviewed by two investigators (Y.X. and G.W.) independently for eligibility. The enrolled articles were excluded as follows: (i) 3D imaging reconstruction; (ii) 3D cell cultured system; and (iii) 3D printing in bioengineering. If the two investigators disagreed about the eligibility of an article, it was resolved by consensus with a third reviewer (G.F.). For the eligible articles included in this study, data were also extracted by two reviewers (G.W. and Y.L.), who reached a consensus on all of the data extraction items.

Personalized 3D-printed models provide a novel way for patient-physician communication and preoperative counseling about complicated conditions and procedures (Figure 1B). 3D-printed kidneys provided to patients resulted in superior survey scores during the patient assessment of their satisfaction and understanding of their own pathology, as well as the surgical procedures, compared to review of 2D imaging alone (3).

The tactile “organ” can also help the students to better understand kidney physiology, anatomy, tumor characteristics, and surgical procedures. 3D-printed kidney-assisted contributes to the R.E.N.A.L. (Radius; Exophytic/Endophytic; Nearness; Anterior/Posterior; Location) nephrometry scoring assessment used by clinical students, when compared to traditional educational tools, reflecting the potential benefits of 3D printing in anatomical education (5).

In addition, 3D-printed kidneys have been utilized as simulators, primarily in partial nephrectomy (PN) simulation via robotic and laparoscopic systems, allowing trainees and junior clinicians the opportunity to improve training quality and reduce learning curves in both safety and effectiveness. The 3D kidney was presented to junior surgeons for preoperative simulation, contributing to their understanding of surgical procedures, and thus improving their surgical performance and patient outcomes (4).

Physical kidney models created by 3D printing can provide precise and individualized physical models that help surgeons to easily understand actual renal tumor characteristics, including tumor size, depth, and the relationship of location to the arteriovenous and collection systems, contributing to preoperative surgical programme determination and intraoperative guidance (Figure 1A) (6). 3D-printed models were welcomed during the performance of complex and high-precision surgeries (Figures 1D,E). The advantages of the 3D kidney for partial nephrectomy (PN) include shorter operation times and warm ischemia times, less intraoperative blood loss, as well as fewer complications, in comparison to PN with imaging alone (9). Our previous data revealed that, compared with traditional laparoscopic partial nephrectomy, 3D-printed models can help to reduce the warm ischemia time and the estimated intraoperative blood loss from 29.2 to 24.6 min, and 131.1 ml to 118.7 ml, respectively, in patients with complex renal tumor (R.E.N.A.L score>8) (8).

Bladder radical cystectomy is a challenging procedure that medical students often experience difficulty with grasping the spatial characteristics of the pelvic region, involving pelvic organs, muscles, vessels, nerves, ligaments, and connective tissue over 2D imaging. 3D-printed models have been utilized in our center to facilitate the recognition of anatomical features within an educational setting and detected significant improvement in student satisfaction with training (Figure 1C). Importantly, the clinical education of students with 3D bladder models was superior to traditional educational methods, in terms of the students' understanding of the anatomy, treatment options, and surgical processes (10).

Another potential utilization of 3D models in bladder cancer is the simulation of transurethral resection of bladder tumor (TURBT). The TURBT model, which consisted of layers of mucosal, muscular, serosal, and perivesical fat, were simulated and demonstrated potential for incorporation of training and maintenance of advanced procedural skills (11). 3D reconstruction of blood supply to urinary bladder proved valuable for mock vascularized composite allograft bladder transplantation (12). Besides, the proposed application of 3D printing technology resides in the ability to evaluate novel Y pouch neobladder about structural and functional reconstructive outcomes (13).

Similar to the applications of 3D printing in renal cancer, 3D prostate models would undoubtedly be useful for patient counseling, student education/training, as well as surgical planning and guidance. Compared to 2D imaging, augmented reality (AR) models and 3D computer models, 3D prostate physical models presented the greatest contribution to patient understanding of their diseases and prostate anatomy, tumor characteristics, as well as surgical procedures. 3D prostate models were also reported to be valuable for medical students but not for expert urologists in plotting tumor locations, since prostate MRI is arguably more difficult to interpret than other imaging (14).

The role of 3D models in assisting with prostate biopsy has the potential to enhance the histological correlation rate for prostate adenocarcinoma, with a detection rate of prostate cancer from 22.4% with systematic biopsies to 46.2% with targeted biopsies. Additionally, 3D-printed prostate models have shown great promise in surgical planning and guidance for tumor resection and may potentially aid in complex nerve-sparing radical prostatectomy, resulting in high accuracy of pathological margins and a promising approach (15).

3D models assistant can overcome the challenges of complex anatomy and pre- and intraoperative sets required for clinical practices, thus allowing utilization in urologic cancer of kidney, bladder, as well as prostate. Apart from previously mentioned uses, proposed application of 3D printing technology resides in the ability to utilized insurgical planning and guidance of adrenal part resection and testicular sparing surgery (Figure 2). With improvements in technology and materials, cost which derived from the initial purchase of the printer and printing materials will result in lower production and equipment costs (2). However, the level of quality evidence on 3D technology reported in the last decade is not high enough. Large-scale evidence and comparative trials are required to elucidate 3D printing's benefits to clinical practices in urology.

YX and GF drafted the article. All authors contributed to its completion.

This study was funded by the clinical research center for renal tumor in Hunan province (2020SK4006).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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