Sentinel lymph node imaging in urologic oncology

Abstract

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.

Sentinel node theory helps tracking of primary lesions of cancers of unknown primary

“…Therefore, when we found a CUP patient with cervical lymph node metastasis with or without supraclavicular lymph node metastasis, as they were in the same direction of lymphatic drainage, we assumed the primary site of this patients lying in the head and neck according to SLN theory. Besides, axillary nodes were often thought to be SLNs of breast cancer [ 27 , 32 ], SLNs of lung cancer were often believed to be hilar or mediastinal nodes [ 33 ], and inguinal lymph nodes were believed to be SLNs of cancer in pelvic cavity like urologic cancer or anal canal cancer [ 34 , 35 ]. We assumed the potential primary site in the same way according to SLN theory and compare it with pathologic results.…”

Iron oxide nanoparticles as multimodal imaging tools

“…uorescence mediated tomography, uorescence reectance tomography, optical coherence tomography, a large number of uorescence microscopies, ow cytometry, spectrophotometry, intra-vital microscopy, intravascular non-invasive near-infrared (NIRF) imaging, clinical endoscopy, and equipment for uorescence detection during surgery. Such method can be used for monitoring magnetofection efficacy, 60 for multi-modal imaging with MPI, MRI and PAI, 61,62 for detecting various biological entities such as tumors, 16,56 apoptotic cells, 7 and sentinel lymph nodes, 4 and for delineating inltrating tumors such as glioblastoma. 63…”

“…Iron oxide nanoparticles (IONP) can be used to image organs/ cells, which capture or accumulate them, such as the liver, 1 spleen, 2 lymph nodes, 3,4 bone marrow, and those of the mononuclear phagocytic system, whether these organs/cells are tumorigenic or not. 5,6 Other examples of IONP imaging applications include the detection of apoptosis, 7 inammation, 8 angiography, 9 ruptured atherosclerotic plaque, 10 multiple sclerosis, 5 integrity of the blood-brain barrier, 11 and vasculature, e.g.…”

Inguinal lymph node dissection for penile cancer: a contemporary review

“…Surveillance of regional LNs is associated with the risk of disease recurrence developing in the future from undetected micro-metastatic disease, as patients with clinically nodenegative disease at the time of diagnosis (cN0) having a risk of micro-metastases to ILNs of approximately 25% (15). This risk can be further stratified according to histopathological features of the primary tumour, and the management of this patient group should be directed by pathological risk factors including local stage, grade and lymphovascular invasion, with the risk of micro-metastatic disease in low and intermediate risk disease of between 17-50% (16,17). Early ILND in cN0 patients offers increased long-term survival compared to delayed lymphadenectomy, with patient survival over 90% with early lymphadenectomy and less than 40% with lymphadenectomy for patients with regional recurrence (18,19).…”