Approximately 75% of newly diagnosed bladder cancers (BCs) are non-muscle invasive BCs (NMIBCs), characterized by a high recurrence rate raging between 50–70% (1). The standard-of-care for patients with NMIBC has been transurethral resection of bladder tumors (TURBT). During TURBT, white light (WL) cystoscopy is the conventional method for detecting BCs; however, its ability to exactly diagnose BCs is not entirely satisfactory due to limitations in visualizing small and/or flat malignant lesions. Therefore, such lesions are sometimes unrecognized without resection under the WL guidance, which could be a possible cause for high postoperative recurrence rate in NMIBC patients (1-3).

In recent years, several types of novelties in imaging technology have been introduced into clinical practice in order to improve clinical outcomes of TURBT for NMIBC patients by detecting tumorous lesions that are missed or inadequately resected due to suboptimal visualization under WL guidance (4-10). Of these, photodynamic diagnosis (PDD) involving the oral instillation of 5-aminolevulinic acid (5-ALA), which is metabolized to the photoactive compound and emits red fluorescence under the blue light (BL) source, is regarded as a promising approach in the improvement of diagnostic accuracy during TURBT for NMIBC patients (7). In fact, there have been several studies showing the superiority of the TURBT using 5-ALA-mediated PDD to that using WL cystoscopy (8-10). To date, however, the utilities of this approach have been investigated by conducting the PDD prior to initiation of conventional WL TURBT, which requires complicated procedures for recording tumorous lesions (11,12), maybe resulting in the achievement of incorrect outcomes in some patients, such as those with multiple tumors.

Considering these findings, we evaluated whether additional resection of fluorescent lesions visualized by 5-ALA-mediated PDD following the complete resection of visible tumors by WL TUR could improve diagnostic accuracy in a total of 83 patients with NMIBC.

Patients. This was a retrospective study including a total of 83 patients with lesions suspicious for BC on preoperative WL cystoscopy who underwent TURBT combined with PDD using 5-ALA and were subsequently diagnosed with NMIBC on pathological examinations at our institution between January 2018 and March 2020. The design of the study was approved by the Research Ethics Committee of our institution, and the need to obtain informed consent to be involved in it from all of the included patients was waived because of its retrospective fashion.

Apparatus for PDD. 5-ALA-mediated PDD was performed using a D-LIGHT System (Karl Storz GmbH & Co., Tuttlingen, Germany), consisting of D-Light C with a filter for transmitting BL, HOPKINSII PDD telescope with a filter for shielding from BL and a video camera system, which enables to switch between the BL and WL modes for the fluorescent and conventional observations, respectively.

Procedure for TURBT combining with PDD. In all included patients in this study, a solution of 5-ALA was orally administrated at 20 mg/kg body weight approximately 3 hours prior to TURBT. TURBT was initially performed with the conventional WL source as previously reported (13). Briefly, under general anesthesia, evidently visible tumors were completely removed, and the muscle layer at the bottom of index tumor was resected in order to prevent residing tumor. After completing the resection of all tumors, PDD with the BL source was then performed, and if fluorescent lesions were detected, these were additionally resected. Finally, a random cold-cup biopsy of vesical mucosa was performed under the WL guidance targeting the trigone, posterior wall, bilateral lateral walls, dome and anterior wall (14). Pathological examinations of resected and biopsy specimens were carried out according to the 2002 American Joint Committee on Cancer TNM system and graded according to the 2004 World Health Organization/International Society of Urologic Pathology classification.

Statistical analysis. All statistical analyses were performed with EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), and p<0.05 was considered significant. Logistic regression analysis was used to evaluate factors that predict the presence of residual cancer lesion by our PDD system after complete resection of visible tumors with the WL source.

Major clinicopathological findings of the 83 patients included in this study are summarized in Table I. As shown in Table II, of these 83, 39 (47.0%) were judged to have fluorescent lesions under the observation by the BL guidance after WL TURBT, while there was no positive finding in the remaining 44 (53.0%). Of the 39 patients with positive findings on the PDD, 20 (51.3%) were diagnosed as having residual cancer by additional resection of fluorescent lesions detected by the BL source. In addition, random biopsy detected cancers in 2 (4.5%) of the 44 patients with negative findings on the PDD, while additional malignant lesions were not diagnosed in the 39 patients positive for the PDD by random biopsies. Therefore, the sensitivity, specificity, positive predictive value and negative predictive value in diagnosing residual cancer lesions by our 5-ALA-mediated PDD system were 90.9, 68.9, 51.3 and 95.5%, respectively.

Univariate and multivariate analyses were then performed to identify parameters associated with the presence of residual cancers following WL TURBT (Table III). Of several parameters examined, the preoperative findings on urinary cytology, tumor multiplicity, pathological T stage and tumor grade were shown to have significant impact on the presence of residual cancer lesions. Of these 4 parameters, only the preoperative findings on urinary cytology were independently related to the diagnosis with the presence of residual cancer lesions by our PDD system.

It has been well characterized that despite comprehensive progress in the management of patients with NMIBC, including diagnosis, treatment and follow-up, they still experience a frequent postoperative recurrence ranging between 50–70%, which may be attributed, at least in part, to overlooking of tumorous lesions, particularly flat and/or small lesions, during conventional WL TURBT (1-3). In recent years, therefore, new imaging technologies, such as PDD and narrow band imaging, have been introduced into TURBR for NMIBC in order to enhance the tumor visualization and to subsequently improve diagnostic accuracy in patients with NMIBC (4-10). In particular, the significance of 5-ALA-mediated PDD during TURBT has been intensively investigated, and its feasibility has been clearly demonstrated (6-10). For example, Hungerhuber et al. analyzed TUR specimens from 4630 lesions, and repotted that of all tumorous lesions, 92.0% were detected by 5-ALA-mediated PDD, while 76.3% were detected under WL guidance (9). Similarly, a multicenter phase III study for 61 NMIBC patients undergoing TUR with orally applied 5-ALA showed that the sensitivity of the BL source was significantly higher than that of the WL source (6). However, these previous studies have conducted PDD prior to WL TURBT, which may make it difficult to clearly record tumorous lesions in some patients, especially those with multiple tumors (11,12), and thus could lead to draw incorrect outcomes in the accuracy of PDD. Considering these findings, we completely resected visible tumors under WL guidance, and subsequently performed 5-ALA-mediated PDD in order to exactly assess whether the PDD could enhance the diagnostic accuracy in patients with NMIBC.

In this series, following the resection of all visible tumors, fluorescent lesions under the BL guidance were detected in 39 of the 83 included patients, and 20 of these 39 patients with positive findings by PDD were diagnosed with residual cancer by additional resection of fluorescent lesions. Accordingly, it could be concluded that at least 20 (23.7%) of the 83 patients benefited from our PDD system. As mentioned above, due to the different timing of the PDD in this study from those in previous studies (6-10), it is difficult to simply compare the outcomes among them; however, the real benefit for accurately diagnosing NMIBC may be achieved in approximately 25% of patients undergoing TURBT combined with 5-ALA-mediated PDD, irrespective of the timing of PDD (6-10). For example, Nakai et al. reported that 25.4% of tumor specimens were diagnosed as positive by the PDD preformed prior to TURBT (6). Collectively, these findings suggest that our PDD system could provide the diagnostic accuracy of NMIBC similar to that in conventional PDD followed by TURBT.

The low specificity in the diagnosis of NMIBC is a well-known disadvantage of the PDD, including that using 5-ALA (15,16). In several previous studies, the specificity of PDD was reported to be approximately 60%, which was generally lower than that of conventional WL examinations (6-10,17,18). Low specificity of PDD reflects high proportion of benign, but fluorescently positive lesions under the BL guidance; therefore, unnecessary resection of such lesions cannot be avoided based on the findings of PDD, resulting in the increase in surgical invasiveness during TURBT. In fact, Stenzl et al. reported that more specimens were resected from patients undergoing TURBT combining 5-ALA-mediated PDD than from those undergoing conventional TURBT alone (18). In this series, however, the specificity of 5-ALA-mediated PDD was 68.9%, which is higher than those in previous studies. This outcome could be explained by complete resection of visible tumors prior to PDD, which may contribute to remove factors leading to low specificity of PDD, such as emphasized autofluorescence and noise effect.

Since there have been insufficient findings with respect to the cohort who are likely to benefit from the PDD, it is of interest to identify characteristics associated with the detection of residual cancers following WL TURBT by our PDD system. Out of several factors examined, a positive finding on preoperative cytology was shown to be independently associated with the presence of residual cancer. This finding is agreeable considering sensitive detection of carcinoma in situ by urinary cytology, which is usually difficult to exactly diagnose by the WL guidance alone (19). Accordingly, it is highly recommended to perform WL TURBT followed by 5-ALA-mediated PDD in NMIBC patients showing positive findings on preoperative urinary cytology.

Herein, although there are several strengths, particularly valuable findings regarding the clinical significance of PDD after TURBT, we would like to describe several limitations of the study. Initially, this was conducted as a retrospective single arm study with a small sample size; therefore, it is necessary to confirm the findings presented in this study by conducting a prospective randomized study including a much larger number of NMIBC patients than those in this study. Secondary, the outcomes of this series were analyzed on patient basis; however, the information examined on tumor basis should also be helpful to further clarify the significance of our PDD system. Finally, this study focused on the diagnostic accuracy of our PDD system, while it will be necessary to investigate whether this system affects the postoperative recurrence by prolonging the observation period.

In conclusion, the findings presented in this study showed that 5-ALA-mediated PDD following standard WL TURBT could improve diagnostic accuracy in patients with NMIBC, particularly those with positive for preoperative urinary cytology. Furthermore, prior resection of all visible tumors may render the subsequent procedure of 5-ALA-mediated PDD simpler, suggesting a possible improvement of specificity in the diagnosis of NMIBC by 5-ALA-mediated PDD.

The Authors declare no conflicts of interest.

Study conception and design: Hideaki Miyake, Keita Tamura, Kyohei Watanabe. Acquisition of data: Kyohei Watanabe, Keita Tamura, Yuto Matsushita, Hiromitsu Watanabe, Daisuke Motoyama, Toshiki Ito, Takayuki Sugiyama, Atsushi Otsuka. Analysis and interpretation of data: Kyohei Watanabe, Hideaki Miyake. Drafting of the manuscript: Kyohei Watanabe, Hideaki Miyake.