The Significance of the Sentinel Lymph Node in Colorectal Cancer and its Isolation with Radioactive Colloid-A Pilot Study
Authors: Antovic Svetozar , Jankulovski Nikola , Stojanovski Sinisa 
Published: November 2016

Introduction.One of the most important factors for prognosis in patients with colorectal cancer (CRC), especially the 5-year survival is the status of regional lymph nodes (RLN). Threfore, today’s recommendations for systematic lymphadenectomy in CRC operations are very important. For correct staging and accepted by all international recommendations, at least 12 LN must be analyzed microscopically. The sentinel lymph node (SLN) is the first lymph node that drains lymph from the tumor and thus represents a LN that has the greatest chance to be the bearer of metastatic disease. Tests to locate the SLN in CRC have started recently and so far there is no consensus on the method for its localization or its significance. The main aim of this study was to improve the tracing of SLN by using radioactive colloid. The secondary aims were to investigate the accuracy, sensitivity and rate of method’s identification. Especially important for the analysis is the significance of SLN and its correlation with other RLN.

Methods.The study is performed at the University Clinic for Digestive Surgery from January 2013 and is still ongoing. A day before the surgery endoscopically around the tumor is injected radioactive colloid with Technetium 99 (Sentiscint Tc 99m Mediradiofarma Ltd) in the amount of 4 ml, which corresponds to 4 mCi (mill curie). Immediately after that, at the Institute of Pathophysiology using a Gamma camera (Mediso DHV nucline spirit), the distribution of the colloid is monitored, which as expected is mostly accumulated in the first LN, that is the genuine sentinel lymph node, thus making lymphatic mapping that is important for identifying possible aberrant drainage. On the day of surgery at 8:00 am, a rerecording with the Gamma camera is made that shows the late distribution of contrast. All patients are operated with standard surgical technique by making resection with systematic lymphadenectomy. Promptly after removing the preparation a Gamma detector probe (Europrobe) is used to determine the radioactivity of the lymph pool and it finds the right SLN which has the highest radioactivity and it is separately sent for complete pathohistological analysis. At the Institute of Pathology all lymph nodes are first treated standardly with HE and then with immunohistochemical method.

Results.So far the study includes 10 patients, 6 men and 4 women, mean age 63 years (59-77). Until now the identification rate is 100%, which means that SLN has been found in all procedures. Only in 2 patients two sentinel lymph nodes have been revealed while the in the remaining only 1, average 1.2. At PH analysis, an average of 14.2 lymph nodes have been isolated (6-25). Only in one patient false negative 1 SLN has been revealed. The number of patients with real negative SLN is 2, which means the SLN is negative and also all the other lymph nodes. The total number of patients with real positive SLN is 7, which means SLN is positive and also some of the other lymph nodes. Therefore the accuracy of the procedure is 90%. The sensitivity of the procedure in our study that is still ongoing, is 87.5%. Up to now there have been no micrometastases detected in these 10 patients with immunohistochemical methods and because of it the up staging for now is 0%. In 2 patients the SLN is the only positive lymph node of all examined LN. In none of the patients aberrant lymphatic drainage has been discovered.

Conclusions.From the results obtained so far in this study, it can be concluded that the identification of the SLN with this method is possible; the accuracy and sensitivity are high and we expect them to be even higher, which is our motive to continue with the study and to analyze minimum 30 patients. We think this would be the highest number of discovered SLN by a surgeon and an institution and we believe it to be sufficient validation of the method.