When is pelvic lymph node dissection necessary before radical prostatectomy? A decision analysis

Purpose: In recent years the role of pelvic lymph node dissection before or at radical prostatectomy has been questioned. We compared the outcome of p erforming or omitting pelvic lymph node dissection in patients undergoing r adical retropubic prostatectomy by formal decision analysis. Materials and Methods: We created a decision tree for patients undergoing r adical retropubic prostatectomy that accounts for all possible branch point s and outcomes. Outcome probabilities applied to the model were derived fro m published data. Utility values were determined for each outcome state by a panel of experts. Decision analysis was done using decision analysis comp uter software. Sensitivity analysis was performed to determine which elemen ts in the model were most important and to calculate threshold values. Results: Using probability data from the literature and our assigned outcom e values, decision analysis initially favored omitting pelvic lymph node di ssection. Sensitivity analysis revealed that the threshold values for the i ncidence of positive lymph nodes and the sensitivity of lymph node dissecti on and frozen section analysis at which outcomes were equivalent were 18% a nd 80%, respectively. Analysis was insensitive to the pelvic lymph node dis section complication rate. Conclusions: We performed formal decision analysis to determine the inciden ce of lymph node metastasis below which pelvic lymph node dissection is not warranted at radical retropubic prostatectomy. Our results suggest that ly mph node dissection is unnecessary in the subset of patients in which the r isk of lymph node involvement is less than 18%.