Therapeutic value of lymph node dissection at radical prostatectomy: a population-based case-cohort study.

OBJECTIVE

• To examine the association between the number of lymph nodes removed in pelvic lymphadenectomy and the risk of prostate cancer death, particularly in low to intermediate risk prostate cancer patients.

PATIENTS AND METHODS

• Data on a subset of patients from a population-based case-cohort study was used to assess the effect of lymph node removal on prostate cancer-specific mortality. • The subset included in this report were those 281 patients from the parent study who were treated with prostatectomy and had a pelvic lymph node dissection and for whom we had a record of the number of nodes removed (the sub-cohort) and 41 patients fitting the same criteria who died of their prostate cancer within 10 years (the cases). • Study variables included number of lymph nodes removed, lymph node status, age, pre-treatment PSA, T category, Gleason score and use of hormonal therapy. • We ran a Cox proportional hazards regression analysis that accounted for the study design and allowed us to consider these patient and disease characteristics as potential confounders of the association of interest. • In a secondary analysis, the results were stratified by nodal status.

RESULTS

• The crude hazard ratio (HR), which is a measure of relative risk, was not statistically significantly associated with a reduction in the risk of prostate cancer mortality as the number of lymph nodes removed at PLND increased (HR: 0.97, 95% CI: 0.91-1.03). • None of the variables considered as potential confounders had an impact on the crude HR. Using two cut points to categorize the number of lymph nodes removed, one at 4 or more removed and the other at 10 or more removed resulted in HRs indicating a risk reduction of 25% in both cases, although these results were not statistically significant. • When we analyzed the association by pathological nodal status, we observed a possible increase in risk in the node-positive group (HR: 1.10, 95% CI: 0.86, 1.42), while those with negative lymph nodes may have benefited from increasing numbers removed (HR 0.95, 95% CI: 0.89,1.02).

CONCLUSION

• The results of this study indicate a possible therapeutic benefit of lymph node removal in node negative patients. Future research should focus on gaining a better understanding of the biologic mechanisms of a possible therapeutic benefit of PLND, particularly for those lower risk patients with histologically negative lymph nodes.