The learning curve for surgical margins after open radical prostatectomy: implications for margin status as an oncological end point

Abstract

Purpose: Surgical margin status is commonly used as an end point for surgical learning. We examined the surgical margin learning curve and investigated whether surgical margins are a good marker for oncological outcome.

Materials and methods: The study cohort included 7,765 patients with prostate cancer treated with radical prostatectomy by 1 of 72 surgeons at a total of 4 major American academic medical centers. We calculated the learning curve for surgical margins and a concordance probability between the surgeon rates of positive surgical margins and 5-year biochemical recurrence.

Results: A positive surgical margin was identified in 2,059 patients (27%). On multivariate analysis surgeon experience was strongly associated with surgical margin status (p = 0.017). The probability of a positive surgical margin was 40% for a surgeon with 10 prior cases, which decreased to 25% for a surgeon with 250 (absolute difference 15%, 95% CI 11 to 18). Learning curves differed dramatically among surgeons. For surgeon pairs the surgeon with the superior positive surgical margin rate also had the better biochemical recurrence rate only 58% of the time.

Conclusions: We noted a learning curve for surgical margins after open radical prostatectomy. The poor concordance between surgeon margin and recurrence rates suggests that while margins clearly matter and efforts should be made to decrease positive margin rates, surgical margin status is not a strong surrogate for cancer control. These results have implications for using the margin rate to evaluate changes in surgical technique and as surgeon feedback.

Figure 1. The surgical learning curve for a positive surgical margin

Predicted probability (black curve) and 95% confidence intervals (gray curves) of a positive surgical margin are plotted against increasing surgical experience. Probabilities are for a patient with typical cancer severity (mean prostate-specific antigen level, pathologic stage, and grade) treated in 1997 (approximately equal numbers of patients were treated before and after 1997).

Figure 2. The surgical learning curve for a positive surgical margin, stratified by presence of organ-confined disease

Predicted probability and 95% confidence intervals (organ confined: black curves; non-organ confined: gray curves) of a positive surgical margin are plotted against increasing surgical experience. Probabilities are for a patient with typical cancer severity (mean prostate-specific antigen level, pathologic stage, and grade) within each group, treated in 1997 (approximately equal numbers of patients were treated before and after 1997).

Figure 3. Learning curve for positive surgical margins, separately by surgeon, for those who performed at least 250 cases

Figure 4. Scatter plot of adjusted probability of 5-year biochemical recurrence versus adjusted probability of positive surgical margins

Each circle represents a single surgeon, and the size of the circle is proportional to the number of patients treated by that surgeon.