Beyond penile cancer, is there a role for sentinel node biopsy in urological malignancies?

The Sentinel Lymph Node in Treatment Planning: A Narrative Review of Lymph-Flow-Guided Radiotherapy

The sentinel lymph node technique is minimally invasive and used routinely by surgeons, reducing the need for morbid extensive lymph node dissections, which is a significant advantage for cancer staging and treatment decisions. The sentinel lymph node could also help radiation oncologists to identify tumor drainage for each of their patients, leading to a more personalized radiotherapy, instead of a probabilistic irradiation based on delineation atlases. The aim is both to avoid recurrence in unexpected areas and to limit the volume of irradiated healthy tissues. The aim of our study is to evaluate the impact of sentinel lymph node mapping for radiation oncologists. This concept, relying on sentinel lymph node mapping for treatment planning, is known as lymph-flow-guided radiotherapy. We present an up-to-date narrative literature review showing the potential applications of the sentinel lymph node technique for radiotherapy, as well as the limits that need to be addressed before its routine usage.

A Drop-in Gamma Probe for Minimally Invasive Sentinel Lymph Node Dissection in Prostate Cancer: Preclinical Evaluation and Interim Results From a Multicenter Clinical Trial

PURPOSE

This study evaluated the performance of a drop-in gamma probe for prostate cancer (PCa) sentinel lymph node dissection (SLND) in a pelvic phantom, porcine model, and in PCa patients as part of an ongoing prospective multicenter clinical trial.

METHODS

Two design variants of the drop-in gamma probe (SENSEI; Lightpoint Medical Ltd) were assessed in the pelvic phantom, and the preferred design was evaluated in a porcine model with clinically representative volumes and 99mTc activities. In the clinical trial, radical prostatectomy, SLND, and extended pelvic lymph node dissection were performed the day after 99mTc-nanocolloid injection and imaging. Sentinel lymph nodes (SLNs) were detected with the drop-in probe and a rigid laparoscopic gamma probe (RLGP). An interim analysis was performed after 10 patients were recruited.

RESULTS

The narrow field of view probe design outperformed the wide field of view design in the pelvic phantom (detection rate, 100% vs 50%). In the porcine model, all activity concentrations could be successfully detected. The drop-in gamma probe successfully detected SLNs in all 10 patients (detection rate, 100%). Two of the SLNs identified by the drop-in gamma probe could not be found with the RLGP. No false-negative cases and no adverse events related to the SLND procedure or the drop-in gamma probe occurred.

CONCLUSION

The drop-in gamma probe meets the usability and performance requirements for SLND in PCa and provides performance advantages over the RLGP. The final clinical study results will confirm the performance of the technique across multiple sites.

Binding indocyanine green to human serum albumin potentially enhances the detection of sentinel lymph nodes. An initial step for facilitating the detection of first-station nodes in penile and other urological cancers

INTRODUCTION

Surgical oncology strives to remove the primary cancer tumor together with its local lymphatic tissue. One of the techniques improving the staging of lymph nodes is sentinel node biopsy. The most common agent used in SNB is indocyanine green (ICG). Indocyanine green is characterized by its high affinity for human serum albumin (HSA). In practice, the visualization of the sentinel node is enhanced by attaching a relatively large carrier to the ICG molecule. The aim of this study was to investigate whether the covalent linking of ICG to a nanocolloid would extend the time of detection of the dye as it binds to HSA, assessed by fluorescence measurements in vitro.

MATERIAL AND METHODS

The influence of the molar concentration of ICG on its ability to form a complex with HSA was investigated. The dye luminescence was measured, with an increasing amount of dye in the presence of a constant concentration of HSA. The stability of the ICG:HSA complex was also investigated.

RESULTS

The binding of ICG and human protein in a solution ratio of 3 : 1 made it possible to detect the ICG luminescence with better and prolonged visibility. In the case of the two lowest ratios, complex formation was not observed. The use of ICG bound to a nanocolloid based on human serum albumin increases the luminescence of the HSA : ICG complex up to 98%.

CONCLUSIONS

Properly selected proportions of human albumin protein and ICH allowed higher and longer luminescence to be achieved. Nevertheless, further studies are necessary to establish the optimal concentration ratio.

An analysis of SPECT/CT non-visualization of sentinel lymph nodes in renal tumors

Background

Sentinel lymph node biopsy (SLNB) after intratumoral injection of ^99mTc labeled nanocolloid and imaging with scintigraphy and SPECT/CT in renal tumors is feasible. However, sentinel lymph node (SN) non-detection rate with scintigraphy and SPECT/CT is high. The aim of the study was to determine factors affecting non-visualization (NV) of SN imaging in renal tumors. Seventy-eight patients with cT1–3 renal tumors received intratumoral injection of 225 MBq ^99mTc-labeled nanocolloid 1 day before (partial) nephrectomy. Radiotracer injection was followed by anterioposterior and lateral scintigraphy in combination with SPECT/CT 20 min and 2–4 h after. Surgical treatment of the tumor with sentinel lymph node biopsy by aid of γ-probe and-camera was performed the next day. Scintigraphy and SPECT/CT images were evaluated and patient, tumor, and procedure characteristics were collected for 73 eligible patients used in uni- and multivariable analysis of a potential association with NV.

Results

A total of 80 (mean 1.1, IQR 0–2, max 6) sentinel lymph nodes in 46 patients were detected with scintigraphy and SPECT/CT. Preoperative visualization rate and intraoperative detection rate was 63% [95% CI 50–73%] and 61% [95% CI 49–72%], respectively. In uni- and multivariable analysis, the only factor associated with non-visualization was age, showing higher odds of non-visualization with higher age.

Conclusion

Our study demonstrated that non-visualization of SNs in renal tumors is relatively high and is associated with patient age. Furthermore, kidneys and also its tumors are highly vascularized which may cause a wash-out effect that could be identified with decreased kidney-liver ratios. However, in our data, the effect was statistically inconclusive. Further studies are needed to improve visualization and standardize the procedure of SLNB in renal tumors. The percentage of NV limits the use of SLNB for research and clinical purposes in renal cancer.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0460-y) contains supplementary material, which is available to authorized users.

Sentinel lymph node imaging in urologic oncology

Lymph node (LN) metastases in urological malignancies correlate with poor oncological outcomes. Accurate LN staging is of great importance since patients can benefit from an optimal staging, accordingly aligned therapy and more radical treatments. Current conventional cross-sectional imaging modalities [e.g., computed tomography (CT) and magnetic resonance imaging (MRI)] are not accurate enough to reliably detect early LN metastases as they rely on size criteria. Radical lymphadenectomy, the surgical removal of regional LNs, is the gold standard of invasive LN staging. The LN dissection is guided by anatomic considerations of lymphatic drainage pathways of the primary tumor. Selection of patients for lymphadenectomy heavily relies on preoperative risk stratification and nomograms and, as a result a considerable number of patients unnecessarily undergo invasive staging with associated morbidity. On the other hand, due to individual variability in lymphatic drainage, LN metastases can occur outside of standard lymphadenectomy templates leading to potential understaging and undertreatment. In theory, metastases from the primary tumor need to pass through the chain of LNs, where the initial node is defined as the sentinel LN. In theory, identifying and removing this LN could lead to accurate assessment of metastatic status. Radiotracers and more recently fluorescent dyes and superparamagnetic iron oxide nanoparticles (SPION) are injected into the primary tumor or peritumoral and the sentinel LNs are identified intraoperatively by a gamma probe, fluorescent camera or a handheld magnetometer. Preoperative imaging [e.g., single-photon emission computed tomography (SPECT)/CT or MRI] after tracer injection can further improve preoperative planning of LN dissection. While sentinel LN biopsy is an accepted and widely used approach in melanoma and breast cancer staging, its use in urological malignancies is still limited. Most data published so far is in penile cancer staging since this cancer has a typical echelon-based lymphatic metastasizing pattern. More recent data is encouraging with low false-negative rates, but its use is limited to centers with high expertise. Current guidelines recommend sentinel LN biopsy as an accepted alternative to modified inguinal lymphadenectomy in patients with pT1G2 disease and non-palpable inguinal LNs. In prostate cancer, a high diagnostic accuracy could be demonstrated for the sentinel approach. Nevertheless, due to lack of data or high false-negative rates in other urological malignancies, sentinel LN biopsy is still considered experimental in other urological malignancies. More high-level evidence and longitudinal data is needed to determine its final value in those malignancies. In this manuscript, we will review sentinel node imaging for urologic malignancies.