Predictability of Near-Infrared Fluorescence Light Sentinel Lymph Node Mapping for Colorectal Cancer Staging

Background: Sentinel lymph node (SLN) mapping using Near-Infrared (NIR) Fluorescence Light is an increasingly used technique to improve nodal staging in several type of tumors, including gastro-intestinal, head and neck, breast and mel- anoma). The ultrastaging has a potential decision-making role in order to propose adjuvant chemotherapies in case of nodal micro-metastases. As a matter of fact, according to the last edition (8th) of the AJCC Cancer Staging Manual, the presence of LFN micro-metastases should directly be staged as N1 and no longer as N1mi. In colorectal cancer, the reported rate of SLN micro-metastases is up to 30%. The aim of this ongoing prospective study is to assess the predictability of NIR fluorescence imaging for ex-vivo SLN mapping in conventional surgical resection for colorectal tumors and the research of micro-metastases in patients with negative node disease (NND). Materials and Methods: Twenty-two consecutive patients presenting resectable colorectal cancer have been prospectively enrolled. All patients underwent a standard oncological laparoscopic resection. The intact surgical specimen was extracted and opened longitudinally and 1 ml of Indocyanine Green (ICG; 5 mg/ml) was injected submucosally at four corners around the tumor in order to identify the lymphatic pathway and the SLNs. Each NND SLN at conventional histological analysis, was further investigated with ultrastaging techniques in order to detect the presence of micro-metastases, including serial sectioning and additional immuno- histochemistry or reverse transcriptase-polymerase chain reaction. Results: Overall, a total of 363 lymph nodes were retrieved. Twelve patients were N?, and 10 were NND. A total of 41 SLN were identified (mean 1.9 per case) and 19 of those were NND. After ultrastaging investigations, no micro-metastases were found in NND SLN, nor in the remaining nodes. SLN located deeper in the mesenteric and mesorectal (even underwent nChRT) fat could easily be identified by NIR fluorescence. Conclusions: In this preliminary series, the sentinel lymph nodes’ asset (both in N ? than in NND) rightly predicts the status of loco-regional nodes, as confirmed by the histological investigations. The absence of micro-metastases in the SLN investigated may be due to the small sample size and more cases should be collected to confirm this finding.