We have demonstrated a learning curve for surgical margins after open radical prostatectomy. A patient treated by an experienced surgeon (250 procedures), compared to a patient treated by an inexperienced surgeon with 10 prior procedures, has an absolute risk reduction of a positive margin of 15%, and a relative risk reduction close to 40%.
There are various lines of evidence to suggest that, although improvements in margin status associated with experience are correlated with those for biochemical recurrence, there is no strong causal association between the two. Firstly, as we have previously reported, the learning curve for recurrence is not importantly affected by adjustment for margins: for example, the absolute risk reduction for 250 versus 10 prior surgeries is was 5.3% after adjustment for margin status, and 7.2% without adjustment. Second, margin status plateaus at about 10% for organ-confined cancer. In contrast, recurrence rates in organ-confined disease continue to improve with increasing experience, with recurrence rates approaching 1% for the most experienced surgeons.
Furthermore, we saw very poor concordance between a surgeon's margin and recurrence rates in this group of academic surgeons. It seems natural to assume that a surgeon with lower positive margin rates than a colleague would also have lower rates of biochemical recurrence. Our data, however, suggest that the two are virtually independent.
This suggests that margin rates and recurrence improve with experience by independent mechanisms. There is a clear and obvious explanation for such a difference: learning for surgical margins, but not biochemical recurrence, involves feedback. Traditional learning theory gives a feedback a central role: in the case of a straightforward task, such as learning to shoot a basketball free throw, individuals learn by directly observing success and failure; for more complex tasks, such as learning to talk, repeated feedback from adults about errors allows children to learn the rules of grammar. In either case, the individual is able to link particular actions to success, others to failure, and thereby improve success rates over time. This is certainly plausible in the case of surgical margins, as the surgeon is told of the patient's margin status relatively soon after surgery, when the memory of the procedure is still fresh, and so may be able to relate a positive margin a particular aspect of the procedure. In contrast, biochemical recurrences occur many years later, at which time the surgeon is unlikely to remember any specifics about the patient's surgery. Improvements in biochemical recurrence rates therefore must occur by some general process of improved surgical technique.
Our findings have several implications. First, it becomes questionable whether margin rates can be used to evaluate changes in surgical technique. The common claim is that a new technique can improve functional outcomes without compromising oncologic control is generally based on equivalent surgical margin rates. Yet if margin rates do not have a strong concordance with biochemical recurrence, it is quite possible for a technique to have similar margin rates but lead to poorer (or conceivably superior) recurrence outcomes. Our findings also have implications for the use of margin rates as feedback for surgeons. It has been suggested that, in an effort to improve outcomes, surgeons might be given data as to their margin rates in comparison to their peers, perhaps adjusted for case mix. Yet if differences in margin rates between surgeons have only a marginal association with differences in recurrence rates, it is questionable whether such feedback would ultimately improve cancer outcomes. Indeed, it is possible that such a system might create an incentive for surgeons to treat low risk cases - many of whom would suffer no ill-effects of their cancer in the absence of treatment - at the expense of patients with high risk cancer, who stand to gain the most from surgery. It is also possible that surgeons told that they have above average margin rates would tend towards a wider excision, with consequent effects on functional outcomes.
The failure of margins to provide an acceptable surrogate for surgical performance seems counter-intuitive. The aim of cancer surgery is, after all, to remove cancer, and a positive margin suggests that cancer has been left in the body. Yet it is clear that some margins are likely artifactual; note, for example, in some series, apical margins had no apparent association with recurrence6
. It is also apparent that the recurrence can occur even if tumor cells are not detected at the edges of the pathologic specimen: in this series, there was a 5% recurrence probability by 5 years for patients with negative margins and organ confined disease. Conversely, a positive margin is far from an inevitable harbinger of recurrence: patients with organ-confined disease but positive margins had greater than a 75% probability of being free of recurrence at 5 years.
Our findings may be taken as contradicting previous work on the importance of surgical margins, including our own prior studies7-8
. This contradiction is more apparent than real. Like previous authors, we did find an overall association between positive surgical margins and biochemical recurrence (hazard ratio of 2.1, p<0.0005, after adjustment for pathologic stage, grade and PSA) and, more specifically, a statistically significant association between a surgeon's margin and recurrence rates. What we are reporting is not that the association is absent, but that it is weak. This is in keeping with prior research. For example, in a recent postoperative nomogram7
, a positive surgical margin has one-quarter of the effect of primary Gleason grade, one-third the effect of seminal vesicle invasion and one-half the effect of extraprostatic extension.