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In colorectal cancer the sentinel node dissection may help to identify any unusual mesenteric lymphatic drainage pattern from the primary tumor site (ex/skip metastases); assuming that accurate pathological staging is critical for therapeutic decisions we are conducing a study to evaluate the feasibility of the sentinel node technique in colorectal neoplasms and its overall accuracy in predicting regional lymph nodes metastases for appropriate staging. From February 2001 to September 2004 we included in this study 30 patients with rectal lesions or degenerate colonic polyps not radically excised by endoscopy. Lymphatic mapping was performed with low molecular weight albumin colloid labelled with 500Mci of 99mTc in a 2 ml volume and injected submucosally by an endoscopic route at the four cardinal points around the tumor, the afternoon before the surgical procedure, both in case of colonic or rectal lesions. Scintigraphic images were obtained with a gamma camera fitted with a general purpose collimator. The day of the intervention, a hand held gamma detecting probe (Scintiprobe m100, Pol-Hi-Tech, Italy) was employed to detect the "hot" nodes, in vivo and ex vivo. These lymph nodes were tagged with a stitch in vivo; the specimen was removed by a standard resection and SLN were dissected ex vivo and sent separately for pathological examination. In case of rectal lesions, the sentinel nodes were searched ex vivo into mesorectal fat in case. All lymph nodes, including blue or hot ones, were embedded separately for preparation of paraffin sections and haematoxylin and eosin staining. Sentinel lymph node were submitted to multi-seriate sections in order to look for micrometastases. Using the radioactive tracer, sentinel lymph nodes were successfully identified in 27 out of 30 patients. Concordance between SLNs and nodal status was observed in 23 out of 27 cases (85%); two patients (7.4%) were upstaged, as SLN was the only site of metastases. In another two cases we observed no concordance between negative sentinel node and non sentinel nodes (false negative rate, 7.4%). Starting from this experience we are proposing a multicentric trial concerning the value of sentinel node technique in rectal cancer and in early colorectal cancers detected by screening programs.

Over the last decade, lymphatic mapping and sentinel lymph node (sN) biopsy have greatly increased the possibility of identifying nodal metastasis in clinically node-negative patients with melanoma and breast cancer, thus improving the accuracy of pathologic staging. Recently, sN biopsy has been applied also in colorectal cancer. This prospective study aimed to assess its feasibility and accuracy in predicting regional lymph nodes metastases in colorectal cancer patients as well as the impact on treatment decision-making.Lymphatic mapping was accomplished by means of blue dye, which was intraoperatively injected into the subserosa overlying the tumor site in 26 patients undergoing colorectal cancer surgery. Following bowel resection, the operative specimen was inspected to identify each blue-stained node, the sN, which was sent separately to the pathologist. One half of each sN was examined by multiple 200 microm sections, while the second half was examined by standard bi-valving technique with hematoxylin-eosin (H and E) staining; all the other regional non-sentinel nodes were routinely examined by standard bi-valving technique and H and E staining.At least one sN was detected in 24 of 26 patients (92.3%); two patients with rectal cancer had no sN identified. Overall, 70 sN were retrieved into the operative specimens, with a mean of 2.9 sNs/patient, and 19 sNs were tumor-positive. An agreement between sN and regional lymph-node status was observed in 20 of 24 patients (83.4%). The sN was histologically negative in two of nine patients with positive regional nodes (sensitivity = 77.8%; false-negative rate of 22.2%); in two of seven patients with tumor-positive sN (28.6%), the sN was the exclusive site of regional nodal metastasis. The negative predictive value was 88.2% (15 of 17 patients), and the overall accuracy was 91.7% (22 of 24 patients). As regards the contribution to the detection of nodal metastasis according to the pathologic technique, standard H and E bi-valving technique detected 16 of 19 tumor-positive sNs (84.2%) while, by means of serial sectioning, metastases were detected in the remaining 3 of 19 sNs (15.8%).The sN biopsy proved feasible, with a rather short learning curve. The focused analysis of the sN by means of serial sectioning improved the detection rate of nodal metastasis compared to standard bi-valving examination, so that a more accurate nodal staging should be expected; finally, an elective localization of metastasis within the sN was observed in almost one third of regional node-positive patients.