The increasing use of imaging techniques, such as computed tomography (CT), ultrasound and magnetic resonance imaging, has led to an increase in the incidental detection of small renal tumors. For small-scale cancers, a partial nephrectomy (PN) or ablation therapy (AT) is highly recommended to preserve kidney function. ATs, such as cryoablation (CA) and radiofrequency ablation (RFA), have emerged as valuable treatment options (1), whereas PN remains the gold standard for the treatment of small renal tumors, particularly for clinical T1a (cT1a, #x003C;4 cm) tumors. Based on major guidelines, ATs are recommended for selected patients deemed unfit for surgery (2,3); however, ATs can achieve favorable oncological outcomes comparable to those of PN (4,5). As ATs may provide outcomes superior to those of PN in selected patients (6-8), the selection between PN and AT for small renal tumors remains a topic of debate, and is affected by multiple factors, such as patient health, preoperative renal function and tumor-associated factors, such as tumor complexity. Although ATs are less invasive and suitable for patients who are deemed unfit for surgery, establishing the criteria for ‘poor surgical candidates’ is challenging. The decision becomes particularly complex when considering older adults or otherwise healthy individuals or younger patients with multiple comorbidities. As regards recovery time and complications, AT is generally associated with a shorter hospitalization period, a reduced operative time, lower morbidity rates and a more rapid recovery than that observed following surgical options (6-8). These advantages are particularly relevant for patients who wish to minimize their downtime or have other health concerns. Although surgery remains the gold standard for numerous patients, some may prefer the less invasive nature of ATs, particularly for small renal masses, for which observation may also be a reasonable option. In some cases, the discretion and experience of the clinician, as well as patient preferences may influence treatment selection (9).

Tumor location also plays a critical role in determining appropriate treatment strategies. Although basing treatment decisions on tumor-associated factors can provide a holistic approach (10), their effect on the selection of nephron-sparing treatment remains uncertain. The present review discusses how tumor-associated factors affect the oncological and functional outcomes of cT1 renal cancers.

High-complexity tumors, such as hilar or endophytic tumors, are associated with a higher risk of negative oncological outcomes and severe complications when treating small renal masses (11). The RENAL Nephrometry Score is commonly used to assess tumor complexity and to aid in treatment approaches for small renal tumors (9-13). The system consists of five factors, and is simple and practical. A previous study supported the usefulness of scoring systems for predicting the oncological and safety outcomes of ATs and PN (14). Schmit et al (14) demonstrated an association between the RENAL score and the outcomes of percutaneous ATs. Patients who experienced treatment failure had significantly higher RENAL scores than those in patients without treatment failure (mean, 7.6 vs. 6.7; P#x003C;0.001) (14). Furthermore, patients who experienced major complications had significantly higher RENAL scores than those in patients without (mean, 8.1 vs. 6.8; P#x003C;0.001) (14).

The Preoperative Aspects and Dimensions Used for an Anatomical (PADUA) score is another system used to assess the tumor complexity. Compared to the RENAL score, the system provides more detailed three-dimensional and anatomical information (15). Takahara et al (15) demonstrated that trifecta achievement in patients with PADUA scores ≥10 was significantly lower than that in those with scores #x003C;10 (68 vs. 86%). However, the aforementioned studies investigated the outcomes of different interventions using different scoring systems (14,15). To date, to the best of our knowledge, no scoring system has been developed to compare the outcomes of both PN and ATs. Although treatment decisions based on tumor-associated factors ensure a comprehensive approach, their effect on nephron-sparing treatment selection remains uncertain.

Several novel scoring systems have been developed or modified to predict the outcomes of each treatment more accurately (16). Gahan et al (17) proposed a modified RENAL score based on AT outcomes, primarily involving percutaneous ATs. In this scoring system, tumor size was scaled down compared to the original scale, reflecting the general trend that tumors treated with ATs are typically #x003C;4 cm (17). Their findings indicated that the modified score was significantly associated with initial ablation success and recurrence rates. However, this modified system may limit direct comparison in patients undergoing PN (17). Additionally, a previous meta-analysis assessing existing scoring systems found that although these systems could predict warm ischemic time and complications, they failed to predict a trifecta achievement in PN (9). Thus, the usefulness of these scoring systems for predicting oncological and functional outcomes of both treatments remain unclear. The ABLATE (A: Axial tumor diameter, B: Bowel proximity, L: Location within the kidney, A: Angle, T: touching, E: extra) and simplified ABLATE scores were developed to predict the probability of complications and oncological outcomes following AT (16). These scores consider the association between renal tumors and adjacent abdominal organs, particularly the colon and intestines. A previous study identified tumor depth as an independent predictor of treatment failure following AT. Compared to PN, tumor location within the body is a more critical factor in determining the feasibility of AT (16).

It may be challenging for any single scoring system to be applied to all small renal tumors to predict outcomes and guide treatment decisions. An independent evaluation of the scoring system components can help interpret the significance of the findings. Larger tumors tend to have higher malignant potential (9). Although previous studies have applied ATs to larger tumors (>4 cm in diameter; cT1b) (18,19), the use of ATs may be challenging, and supporting evidence remains limited. Even in cT1a tumors, larger tumor size is a predictor of poor prognosis (20,21). ATs are generally considered for tumors #x003C;3-4 cm in diameter. Optimal results are typically achieved for tumors sized #x003C;4 cm, with some guidelines supporting ablation as a primary treatment option for tumors #x003C;3 cm in size (2,3).

Tumor location relative to the polar line is also a component of the scoring systems (11). Owing to their proximity to major vessels and the collection system, hilar tumors require careful consideration to minimize significant complications (11). However, major vessels near tumors can undermine the effectiveness of AT. The heat sink effect can reduce the efficacy of RFA, whereas in CA, the increased temperature due to vessel flow can lead to inadequate ablation (22). Furthermore, hilar tumors often exhibit more aggressive malignant potential (9), thereby affecting oncological control.

Proximity to the collecting system may also affect treatment choice. Among ATs, CA appears to have a lower effect than RFA does on the urinary tract (22). However, Lagerveld et al (23) demonstrated that proximity to the collecting system significantly predicted postoperative complications following laparoscopic CA. Another study that included various AT devices identified renal sinus proximity as a risk factor of local recurrence (24). Given these findings, PN may be a preferred approach for tumors near major vessels and the collecting system, although the current evidence remains insufficient to draw definitive conclusions (25).

Endophytic tumors pose additional challenges due to their location within the normal parenchyma. Theoretically, PN may cause greater damage to normal renal tissue than AT, leading to intraoperative bleeding and post-operative renal impairment. Advanced imaging may facilitate the visualization of endophytic tumors, rendering image-guided percutaneous AT a potentially superior approach (26). Percutaneous CA (PCA) is particularly effective for completely endophytic tumors due to its ability to visualize the ice-ball margins. Although several studies support the feasibility and safety of robot-assisted partial nephrectomy (RAPN) for completely endophytic tumors, available evidence is limited (27).

Tumor size and location within the kidney are crucial for determining the feasibility and success of PN and AT, and a multidisciplinary approach that considers tumor characteristics, patient conditions and preferences is necessary. Proximity to the collecting system, renal sinus, or other critical structures affects treatment decisions. For completely endophytic tumors, image-guided AT may provide outcomes comparable to those of PN, although further investigations with matched backgrounds are required. Despite the promising results of AT, surgery remains the gold standard in numerous cases, particularly for larger tumors or when long-term oncological control is a priority. Further studies with matched backgrounds for the two treatment types, such as randomized controlled studies, are desirable.