Sentinel node mapping during laparoscopic distal gastrectomy for gastric cancer
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- Sporn, E., Davis, J.W., Thaler, K. et al. Surg Endosc (2008) 22: 2097. doi:10.1007/s00464-008-9991-z
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With interest, we read the article by Orsenigo et al.  on sentinel node mapping during laparoscopic distal gastrectomy for gastric cancer. This study enrolled 34 patients, 14 of whom had positive lymph nodes. Only five of these patients had at least one metastatic lymph node among the sentinel nodes identified with a sensitivity of 36%. A subgroup analysis was performed with only three patients who had positive lymph nodes in early cancer, and a positive sentinel node was found in all. The authors then concluded that sentinel node mapping in early cancer is feasible and accurate with a sensitivity of 100%.
Subgroup analysis always needs to be approached with caution [2, 3], but with a sample size of three, this analysis becomes meaningless. To substantiate this, we have calculated the 95% confidence interval for sensitivity using a Bayesian approach with a noninformative prior. The central confidence interval is 0.398 to 0.994, and the shortest confidence interval is 0.473 to 1.00. Both confidence intervals are very wide, reflecting the uncertainty associated with having a sample size of three. Note that both intervals contain 0.5 as a possibility, so the true sensitivity could in fact be as accurate as flipping a coin. Thus, these results should be viewed with tempered enthusiasm.