Association between lymph node density and disease specific survival in patients with penile cancer.

PURPOSE: We assessed the value of lymph node density for predicting disease specific survival after lymphadenectomy for penile cancer.
MATERIALS AND METHODS: Data were collected retrospectively in 75 and prospectively in 88 consecutive patients with squamous cell carcinoma of the penis treated at M. D. Anderson Cancer Center between 1979 and 2007. We identified 45 patients with penile cancer and nodal metastasis who underwent lymphadenectomy with curative intent. Lymph node density was analyzed as a categorical variable by grouping patients into 2 or 3 categories based on equal percents. We explored the prognostic value of lymph node density for predicting disease specific survival in this cohort.
RESULTS: Median followup was 23.7 months in all patients. By the time of analysis 22 patients had died, including 18 (82%) of penile cancer and 4 (18%) of other causes. Median lymph node density in patients alive or dead of other causes was 3.4% (IQR 2.9-5.9) compared to 43.3% (IQR 15.6-80) in those dead of disease (p <0.001). Median lymph node density in all patients was 6.7%. Estimated 5-year disease specific survival in patients with lymph node density 6.7% or less was significantly better than that in patients with lymph node density greater than 6.7% (91.2%, 95% CI 53.9-98.8 vs 23.3%, 95% CI 7.0-45.1, p <0.001). In models comparing lymph node density to known prognostic features lymph node density remained statistically significant, while the other factors were no longer statistically associated with disease specific survival.
CONCLUSIONS: Lymph node density proved to be a significantly better prognosticator of disease specific survival than the current TNM nodal staging system in patients with penile cancer and nodal involvement. Further independent validation is required to determine the clinical usefulness of lymph node density in this patient population.