Re: Raj Satkunasivam, Sheaumei Tsai, Sumeet Syan, et al. Robotic Unclamped “Minimal-margin” Partial Nephrectomy: Ongoing Refinement of the Anatomic Zero-ischemia Concept. Eur Urol 2015;68:705–12

We read with great interest the article by Satkunasivam and colleagues [1] describing the novel technique of robotic unclamped “minimal-margin” partial nephrectomy (PN) and the subsequent letters to the editor regarding this paper [2] and [3]. The technical refinements of the novel technique are (1) complete elimination of all vascular clamping and (2) tumor excision with a minimal margin adjacent to the tumor capsular edge, aiming to maximize functional parenchymal mass preservation while ensuring oncologic efficacy. The amount of vascularized nephron mass preserved appears to be a primary (surgically modifiable) determinant of functional recovery after PN [4], and although possibly determined by the tumor's size and location, it is ultimately linked to the resection technique performed for tumor excision [5]. In this regard, although the PN dogma has always advocated removal of a rim of uninvolved renal parenchyma to ensure oncologic efficacy [6] and despite the trend toward a reduction of the tumor-free “safety” margin thickness in past years [7], no standardization has been achieved to date in detailed reporting of tumor excision in PN series. As such, the debate about the oncologic safety of enucleative PN versus so-called standard PN is ongoing [2], [3], and [8]. However, the oncologic safety of enucleative PN has been confirmed by several studies showing local recurrence-free and cancer-specific survival rates comparable to standard PN [8], [9], and [10]. Moreover, there are currently no evidence-based contraindications for enucleative PN, with the only possible exception of Fuhrman grade IV renal tumors [11]. The article by Satkunasivam and colleagues and the subsequent letters offer insights for further consideration [1], [2], and [3]. In the “Surgery in Motion” video on robotic unclamped minimal margin PN, the tumor pseudocapsule is readily evident throughout the dissection, and it does not appear that the minimal-margin concept is at all different from enucleation; therefore, minimal-margin PN somehow resembles enucleative PN [2]mm) mm (range: 1–9 . At the same time, minimal-margin PN is not unequivocally enucleation, and the sliver of normal parenchyma on the tumor is readily evident during the dissection, resulting in a parenchymal margin width of 1 [1]; however, enucleative PN does not imply, by definition, a 0-mm parenchymal margin [3], [12], and [13]. After all, what are the truly significant questions regarding tumor excision during PN, beyond mere academic discussions of each technique name? Is it really true that “zero-ischemia minimal-margin PN is not enucleation—not in concept, not in technique, and not in surgical margin width” [3]? To answer, we believe a change of perspective is needed. In this paper, we propose a comprehensive model to catch the “whole picture” of tumor excision during PN, aiming to increase the quality of reporting future nephron-sparing surgery (NSS) data (Fig. 1). Fig. 1 Resection strategies (RSs) and resection techniques for tumor excision during partial nephrectomy. The preoperative strategy for tumor excision can be conceptually divided into two clearly defined options based on the choice of the surgeon to develop or not develop the anatomic dissection plane: anatomic versus nonanatomic. If the anatomic plane is developed, then a spectrum of anatomic RSs, including a pure enucleative or a minimal margin strategy, can be outlined. In contrast, if tumor excision is carried out by sharp dissection through the healthy renal parenchyma (thus following different nonanatomic planes), then a variety of nonanatomic RSs, including a macroscopic margin or a wedge RS, can be defined.surface–intermediate–base margin score. = resection technique; SIB = resection strategy; RT = healthy renal margin; RS = HRM Tumor excision during PN is a complex surgical task. Even if detailed data on the tumor's anatomic characteristics are available, it is difficult to formulate a priori the technique to use for tumor excision from its overall behavior. Both enucleative and minimal-margin resection strategies take advantage of the key anatomic features of the tumor–parenchyma interface [14] and [15]. Specifically, both strategies are grounded in the following anatomic bases: (1) the natural radially oriented architecture of the kidney parenchyma and intrarenal vasculature; (2) the presence of a distinct fibrous pseudocapsule in the vast majority of renal tumors; (3) the histologic modifications at the tumor–parenchyma interface, including glomerulosclerosis, nephrosclerosis, and arteriosclerosis; and (4) the generally smaller caliber and fewer number of intrarenal vessels in this histologically altered zone immediately adjacent to the tumor edge [1] and [14]. The inherent characteristics of the tumor–parenchyma interface allow definition of a constant anatomic dissection plane that can always be identified and bluntly developed in close vicinity to the tumor capsule, with or without the removal of a sliver of healthy renal tissue. As such, the anatomic dissection plane is a key landmark during PN and appears histologically and oncologically safe for tumor excision, with the least chance of hemorrhage [1]. Nonetheless, there are currently no standardized instruments to manage the complexity of tumor excision during PN, leading to loss of relevant information in the published NSS series. What is the surgeon's dissection strategy, and how is the dissection plane developed according to the specific tumor and patient characteristics? The debate about the merits and limitations of different PN resection techniques will continue to increase if no standardized descriptors of tumor excision are used [8]. Although the strategy used for tumor excision (resection strategy) is inherently connected to the surgeon's (or institution's) intent or personal belief, the final resection technique depends on several tumor- and patient-related variables. It is essential to clearly divide the concept of resection strategy, that is, the preoperative intent of the surgeon, from that of resection technique—the actual postoperative surgical result (Fig. 1). The resection strategy described by Satkunasivam and colleagues would be classified as “anatomic, minimal-margin,” as the technical aim is to develop the anatomic dissection plane maintaining a 1-mm sliver of parenchymal tissue on the tumor capsular surface rather than completely baring the capsule [1]. In contrast, the classification of the actual resection technique can be done only after surgery, according to careful analysis of the intrarenal portion of the specimen. In this regard, the surface–intermediate–base (SIB) margin score has been proposed recently to provide the literature with a standardized reporting system of resection techniques during NSS [16]. The model was recently validated from a histopathologic perspective showing that the visual definitions of resection techniques used to calculate the score significantly mirror histopathologic analysis to quantify and report the thickness of healthy renal margin resected by the surgeon [12]. According to the video frames showing the inner surface of the resected tumor (minutes 11:47 and 12:06 of the “Surgery in Motion” video), the resection technique presented by the authors and defined as minimal-margin PN [1] might have been classified as hybrid enucleation (SIB score 2). We believe the surgeon's resection strategy might be a strong determinant of the pattern of resection techniques performed at the time of PN and might even be correlated to each technique's results. Further research should evaluate the contribution and the possible interrelationships of resection strategy, resection technique, and surgical expertise for ultimate NSS outcomes. In summary, the ultimate goal of PN is complete excision of the tumor with negative margins while maximizing preservation of vascularized parenchyma. In this regard, we agree with Satkunasivam and colleagues that individualized tailoring of the excision plane based on intraoperative assessment of the peritumoral tissue planes will be the key concept of future PN techniques [3] and [12]. However, we strongly believe that resection technique might be different from resection strategy and that routine assessment of tumor excision descriptors using standardized reporting models should be mandatory in future PN series to compare the outcomes of different surgical techniques in a meaningful way. Further research is needed to define the optimal strategy for tumor excision during PN according to the specific anatomic characteristics of each renal tumor. Because most previous studies comparing different techniques for tumor excision were retrospective and possibly biased by lack of standardized classification of resection techniques [11] and [17], a need for randomized controlled trials (RCT) is often claimed [2] and [8]; however, whether an RCT is really needed to solve the enucleation-versus-enucleoresection dilemma is still controversial [3] and [18]. In particular, because the resection strategy does not necessarily translate into the expected resection technique at the time of PN, how can the randomization process between enucleation and enucleoresection be made a priori? A standardized assessment of the actual resection technique can be done, by definition, only after surgery [16]. Our perspective is that tumor excision is PN and that a well-designed, prospective cohort study including careful assessment of both resection strategy and resection technique through a comprehensive reporting model (Fig. 2) might be the most thoughtful way to address this controversial topic. Fig. 2 Standardized reporting of key tumor excision features during partial nephrectomy.surface–intermediate–base margin