Technical details of sentinel lymph node mapping in colorectal cancer and its impact on staging

Background: Sentinel lymph node (SLN) mapping for melanoma and breast cance r has greatly enhanced the identification of micrometastases in many patien ts, thereby upstaging a subset of these patients. The purpose of this study was to see if SLN mapping technique could be used to identify SLNs in colo rectal cancer and to assess its impact on pathological staging and treatmen t. Methods: At the time of surgery, 1 ml of Lymphazurin 1% was injected subser osally around the tumor without injecting into the lumen. The first to four th blue nodes identified were considered the SLNs, which have the highest p robability to contain metastases. A standard oncological resection of the b owel was then performed. Multilevel microsections of the SLNs, including a detailed pathological examination of the entire specimen, was performed. Results: SLN was successfully identified in 85 (98.8%) of 86 patients. In 8 5 patients, there were 1367 (16 per patient) lymph nodes examined, of which 140 (1.6 per patient) were identified as SLNs. In 53 (95%) of 56, of whom the SLNs were without metastases (negative), all other non-SLNs also were n egative. In 29 (34% of 85) patients, SLNs were positive for metastases; in 14 of the 29 patients, other non-SLNs also were positive in addition to the SLNs. In the other 15 of the 29 patients (18% of 85 patients), SLNs were t he only site of metastases, and all other non-SLNs were negative. In 7 pati ents (8.2% of 85 patients), micrometastases were identified only in 1 or 2 of the 10 sections of a single SLN. In five of seven patients, such microme tastases were detected by hematoxylin and eosin staining and immunohistoche mistry; in the other two patients, it was detected only by immunohistochemi stry. In patients with negative SLNs, the rate of occurrence of micrometast ases in non-SLNs was 5 (0.4%) of 1184 lymph nodes. Conclusions: SLN mapping can be performed easily in colorectal cancer patie nts, with an accuracy of more than 95%. The identification of submicroscopi c lymph node metastases by this technique may have upstaged these patients (18%) from stage I/II to stage III disease, who may then benefit from furth er adjuvant chemotherapy.