A New Formula for Prostate Cancer Lymph Node Risk

Introduction: The successful treatment of prostate cancer depends on the accurate estimation of the risk of regional lymph node (LN) involvement. The Roach formula (RF) has been criticized as overestimating LN risk. A modification of the RF has been attempted by other investigators using simplified adjustment ratios: the Nguyen formula (NF).

Methods and Materials: The National Cancer Institute Surveillance, Epidemiology, and End Results database was investigated for patients treated in 2004 through 2006 for whom at least 10 LN were examined at radical prostatectomy, cT1c or cT2 disease, and prostate-specific antigen (PSA) <26 ng/ml (N = 2,930). The Yale formula (YF) was derived from half of the sample (n = 1,460), and validated in the other half (n = 1,470).

Results: We identified 2,930 patients. Only 4.6% of patients had LN+, and 72.6% had cT1c disease. Gleason (GS) 8–10 histology was found in 14.4% of patients. The YF for prediction of %LN+ risk is [GS – 5] × [PSA/3 + 1.5 × T], where T = 0, 1, and 2 for cT1c, cT2a, and cT2b/cT2c. Within each strata of predicted %LN+ risk, the actual %LN+ was closest to the YF. Using a >15% risk as an indicator of high-risk disease, the YF had increased sensitivity (39.0% vs. 13.6%) compared with the NF, without a significant reduction in specificity (94.9% vs. 98.8%). The NF was overly restrictive of the high-risk group, with only 2% of patients having a >15% risk of LN+ by that formula.

Conclusion: The YF performed better than the RF and NF and was best at differentiating patients at high risk for LN+ disease.