A post‐radical‐prostatectomy nomogram incorporating new pathological variables and interaction terms for improved prognosis
Authors: O’Brien Beverley A. , Cohen Ronald J. , Wheeler Thomas M. , Moorin Rachael E. 
Published: August 2010

Study Type – Prognosis (systematic review) Level of Evidence 2a

What’s known on the subject? and What does the study add?

Nomograms are commonly used by urologists to assess a patient’s risk of developing biochemical failure (PSA recurrence) after radical prostatectomy. The nomograms currently available on websites and in the published literature do not take into account recent developments in pathological reporting which may improve our ability to more accurately predict patient prognosis. Furthermore, currently available nomograms treat all clinical predictors as independent variables without considering the possibility that these factors may be interlinked, which may alter their predictive value.

Our study assesses the predictive value of several new pathological variables and demonstrates that the per cent of Gleason patterns 4 and/or 5 (% 4/5), intraductal prostatic carcinoma and prostate weight significantly improve the predictive value of a model based on established pathological variables. We also show that consideration of interactions between % 4/5, surgical margin status and extracapsular extension further improves our accuracy in predicting patient PSA recurrence. Finally, we find that published nomograms based on PSA recurrence defined as ≥0.4 ng/mL provide over‐optimistic predictions for prostate cancer patients where PSA recurrence was defined as ≥0.2 ng/mL.

OBJECTIVE

To evaluate new variables in prostate pathology reporting including, the per cent of Gleason patterns 4 and/or 5 (% 4/5), presence or absence of intraductal carcinoma of the prostate (IDCP), tumour volume and the prostatic zone of tumour origin as predictors of post‐radical‐prostatectomy (RP) biochemical recurrence (BCR).

To develop an optimal postoperative nomogram for patients with prostate cancer.

PATIENTS AND METHODS

Our study cohort was 1939 eligible patients from the Abbott West Australian Prostatectomy Database.

Multivariate Cox proportional hazard regression models were developed to predict BCR which was defined as prostate‐specific antigen (PSA) ≥0.2 ng/mL.

Our models and the 2009 Kattan postoperative nomogram were compared in terms of discrimination and calibration, with internal validation of our final model performed using bootstrapping methods. Our final model is presented as a nomogram.

RESULTS

The Kattan nomogram was accurate in discriminating our patients according to risk (concordance index: 0.791) but calibration analysis indicated underestimation of patient risk, particularly for high‐risk disease.

Our nomogram incorporates % 4/5, IDCP and prostate weight plus interaction terms between % 4/5, positive surgical margins and extracapsular extension, giving improved predictive accuracy (concordance index: 0.828) and calibration.

CONCLUSIONS

Nomograms that predict risk of BCR defined as PSA ≥0.4 ng/mL may not be optimal for patient cohorts where BCR is defined as PSA ≥0.2 ng/mL.

If our findings are validated in other populations, current post‐RP nomograms may be improved to a modest degree by incorporating the new variables prostate weight, IDCP and % 4/5, and by considering interactions between predictive variables.