Objectives: To study the relation between the number of removed and examined lymph nodes at pelvic lymph node dissection and the rate of lymph node invasion (LNI).
Methods: A total of 858 patients aged 45 to 85 years were predominantly treated with extended pelvic lymph node dissection before radical retropubic prostatectomy. The pretreatment prostate-specific antigen level was 0.24 to 49.9 ng/mL (median 5.8). Most lesions were Stage T1c (55.2%) or T2 (40.7%), with a biopsy Gleason sum of 6 or less (62.2%) or 7 (25.1%). Receiver operating characteristic curve coordinates were used to determine the probability of finding LNI according to the number of removed and examined lymph nodes. Moreover, the association between the number of removed lymph nodes and LNI was tested in univariate and multivariate logistic regression models.
Results: From 2 to 40 nodes (mean 15, median 14) were removed and examined, and 88 patients (10.3%) had LNI. The LNI rate increased with the number of removed nodes (P <0.001): 2 to 10 nodes removed, 5.6% LNI rate; 10 to 14 nodes removed, 8.6% LNI rate; 15 to 19 removed, 10.2% LNI rate; and 20 to 40 removed, 17.6% LNI rate. On multivariate analysis, the number of examined nodes predicted for LNI (P <0.001), after accounting for prostate-specific antigen level, clinical stage, and biopsy Gleason sum. The receiver operating characteristic coordinate plot indicated that the removal of 28 nodes yielded a 90% ability to detect LNI. Conversely, the assessment of 10 or fewer nodes was associated with a virtually zero probability of finding LNI.
Conclusions: We have provided a critical assessment of the concept that the nodal yield at pelvic lymph node dissection is closely associated with the rate of LNI.