Glen Tisman, MD: Nomograms – Probability of Seminal Vesicle Involvement

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Nomogram 2
Probability of Seminal Vesicle Involvement

Koh et al2 presented Nomogram 2 which they used to predict the chance for seminal vesicle involvement (SVI). Patients with seminal vesicle involvement by tumor are considered by most urological surgeons to be inoperable because of a high chance of metastatic spread and so are better treated by other means. Koh analyzed a retrospective cohort of 763 patients with clinical stages T1c–T3 prostate cancer who were diagnosed by systematic biopsy and treated with radical prostatectomy. They recorded the location of each biopsy core and measured the length of cancer and total length of each core. Using logistic regression analysis, they constructed and internally validated a nomogram to predict SVI.

A total of 60 patients (7.9%) had SVI. Cancer was present in a biopsy core from the base in 437 patients, of whom 12.8% had SVI compared with only 1.2% of the 326 without cancer at the base. None of the 275 patients with PSA <10 ng/ml and no cancer at the base had SVI. On multivariate analysis, serum PSA (p <0.0005), primary Gleason grade (p <0.028), and percent cancer at the base (p <0.005) were the only significant predictors of SVI. The predictive accuracy of a standard model that included only stage, grade, and PSA was maximally enhanced by including the percent cancer at the base (p <0.0013). A nomogram that incorporated this variable produced probabilities of SVI that differed from the standard model by <10% in 68% of the cases.

Accordingly, Koh et al concluded that the presence and amount of cancer in systematic needle biopsy cores from the base of the prostate strongly predicts the presence of SVI.

Clinical scenario 2

Clinical scenario 2: Using Nomogram 2, let us now enter data for a patient presenting with a PSA = 6 ng/ml (85 points, which is derived by vertically drawing a line from the PSA line at the 6 value up to the Points line (the point of intersection is the value of 85). Also, the patient has a T2a tumor (0 points), a primary Gleason grade of 4 (7 points), a secondary Gleason grade of 3 (6 points), and 50% of cancer in prostate base biopsy cores (15 points). The total points are 113. Dropping a line from the Total Points line at 113 intersects the Probability of SVI line at the 0.15 or 15% value. Thus, there would be a 15% risk for SV invasion in this patient. Conversely, had the patient had a T2a tumor with a primary Gleason grade = 3 (0 points), a secondary Grade 3 (5 points), a PSA of 4 (77 points) with no base biopsy cores positive for tumor (0 points) (total points = 82) then Nomogram 2 would predict a 0% risk for seminal vesicle involvement. Patients with tumor extension to the seminal vesicles frequently relapse with extraprostatic metastases.

2. Koh H, Kattan MW, Scardino PT, et al A Nomogram to predict seminal vesicle invasion by the extent and location of cancer. The Journal of Urology, Vol. 170, 1203–1208.

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