In this sample of 994 women with DCIS, for whom we had rich clinical and nonclinical data, ipsilateral event-free survival was predicted by surgical treatment, margin status, and receipt of radiation therapy. BCS in the absence of radiation therapy resulted in substantially lower ipsilateral event-free survival than either BCS followed by radiation therapy or mastectomy, regardless of margins, confirming the role of radiation therapy in the treatment of DCIS demonstrated in randomized controlled trials (9
). BCS with radiation therapy also resulted in lower disease-free survival rates than mastectomy. Regardless of treatments, positive or close margins following the last surgical treatment substantially compromised ipsilateral event-free survival. Because close or positive margins were far more common following BCS than mastectomy, margin status contributed to the superior outcomes of mastectomy relative to BCS. Indeed, an important finding of our work is the large difference in subsequent breast event rates following BCS with positive margins, pointing to the value of additional surgery to achieve negative margins in these cases. Nevertheless, even among subjects with negative margins, we found that ipsilateral event-free survival following mastectomy was substantially greater than following BCS with radiation therapy. This increased risk of subsequent ipsilateral events may be offset, however, by patient preferences for breast preservation.
We found that there were substantial differences by surgeons in surgical treatment, receipt of radiation therapy, and margin status, the three most important predictors of ipsilateral event-free survival in our outcomes model. Other investigators have similarly identified a role of surgeons in the selection of surgical procedure (26
) and in the use of radiation therapy after BCS in the management of DCIS (5
). Our findings suggest that this variation across surgeons is substantively important. Simply by increasing surgeons’ rates of radiation therapy to no less than the sample mean, the overall receipt of radiation therapy could be increased by nearly 15%.
Similar models that predicted margin status, controlling for the detailed clinical and nonclinical factors, found very large unexplained differences by surgeon. We found that positive margins and close margins could be reduced by, respectively, 46% and 25% if all surgeons had positive and close margin rates no greater than the sample means.
Because of the importance of treatment choice and margin status in predicting outcomes, these unexplained differences by surgeon could have profound implications for health outcomes. With reductions in variation by surgeon, based only on changes among those surgeons with low rates of radiation therapy and high rates of positive or close margins, we found that ipsilateral 5- and 10-year event rates could be reduced by 15%–30%. These results have important implications about processes of care, decision making, and ultimately the quality of care for DCIS.
This study had several limitations. Although we found surgeon effects to be robust to the inclusion of the rich set of clinical and nonclinical measures and to the choice of model specifications, these differences by surgeon could be explained by other unobserved clinical or nonclinical factors. Our study was retrospective and our data did not include either the extent of the margin involvement or the number or location of margins involved, either of which could contribute to treatment variations by surgeon. Patient preferences about care (also unobservable to us) could be related to the choice of treating surgeon, consequently generating unexplained differences by surgeon. For example, a surgeon could develop a reputation for aggressively pursuing breast conservation, attracting patients who would, ceteris paribus, prefer to avoid mastectomy. If unrelated to any of our observable measures, this sort of patient-surgeon matching could generate variation in treatments across surgeons that is not strictly attributable to surgeon recommendations. Not only could this matching affect initial surgical choice and the decision to pursue subsequent breast-conserving procedures (re-excisions), but it could also explain the decision to decline additional surgery with close or positive margins. Depending on a woman's preferences, each of the decisions could be optimal, particularly if made with full information about the consequences.
Variation in decision making by surgeons could also, however, account for the large differences by surgeon. The variation could reflect differences in surgeons’ knowledge, attitudes, and beliefs, resulting in differences in treatments or margins for women who appear similar and who have equivalent preferences. For example, surgeons’ beliefs regarding the importance of breast conservation or the threat of DCIS, given lack of natural history data, could generate different recommendations for care that are not consistent with differences in women's preferences. Similarly, surgeons’ recommendations might vary based on their assessments of patients’ ability to adhere to adequate follow-up care.
Whether through differences in surgical technique or differences in beliefs about the importance of negative margins after surgery for DCIS (or both), the independent effect of surgeon on margin status, after controlling for extensive clinical and nonclinical factors, is striking. There is currently no consensus on what constitutes a negative margin (25
). The width of the surgical margin—and the decision to stop surgical treatment with persistently close or positive margins—may be related to surgeons’ aggressiveness with respect to the size of the excision specimen and the location of the lumpectomy cavity combined with their willingness to offer or recommend re-excision, particularly if the surgeons believe that patients will consider the need for additional surgery as a medical error. Failure to achieve negative margins could indicate an a priori need for mastectomy, implying a failure of the breast conservation therapy strategy in a given patient. Lack of knowledge about the importance of margins, and differences in beliefs about the role of radiation therapy in local control, together with differences in physician–patient communication during the decision-making process could explain the substantial variation in the acceptance of positive margins and the determination not to proceed to mastectomy.
Differences in financial incentives, such as relative reimbursement rates for BCS and mastectomy, could induce differences in surgical treatment (29
). Similarly, insufficient reimbursements for performing re-excision could result in too few efforts to achieve negative margins. We controlled for patients’ insurance status and other socioeconomic status measures in our models, however, and found very little evidence that treatment choices were influenced by insurance.
The substantial variation in receipt of radiation therapy by surgeon is also a concern. The strength of referral relationships between treating surgeons and radiation oncologists could explain differences in rates of radiation therapy by surgeon in that such relationships may affect referral rates or the type of discussions held with patients about the role of radiation therapy. Surgeons may also vary in the degree of logistic support available in their practices to track referrals and follow-up after referral (30
). In addition, surgeons’ beliefs about the importance of radiation therapy in improving the short- and long-term outcomes after surgery for DCIS have been shown to vary (5
). Although we have shown that radiation therapy substantially increases ipsilateral event-free survival following BCS regardless of margin status, it is particularly alarming that there is not a strong relationship between margin status and receipt of radiation therapy.
Our work quantifies the important relationships among treatment choice, margin status, and ipsilateral event-free survival and identifies substantial unexplained variation in treatment choice and margin status across treating surgeons. Our results raise questions that go beyond our data. Why are patients willing to complete surgical treatment with close or positive margins? Is it because they are unwilling to undergo re-excision or mastectomy or because they are uninformed about the presence of or consequences of positive margins? How are the consequences of close or positive margins presented to patients by their surgeons, and is the presentation influenced by the surgeons’ confidence that radiation therapy can adequately provide local control? The latter is particularly interesting in light of the weak relationship we found between margin status and the receipt of radiation therapy among women who received BCS.
Because these decisions have important health outcomes consequences, it would be unsettling if the variation in surgeon effects were not a reflection of differences in women's preferences about the relative merits of risk and breast conservation. Our work, however, provides no evidence regarding patient–surgeon interactions and, more specifically, whether surgeons or patients are ultimately responsible for the variation in treatments. Nevertheless, an important implication of our work is that surgeons may play a critical role both in the surgical treatment choices made by patients (the initial choice to pursue BCS and subsequent re-excisions) and in the receipt of radiation therapy. Because these are the most important factors in predicting outcomes (particularly margin status and receipt of radiation therapy), the substantial variation by surgeon suggests that the quality of DCIS care could be improved.