We found that current practice with respect to PMRT across the NCCN centers generally follows the best available evidence as synthesized in NCCN guidelines. Only 16% of women who were at high risk for disease recurrence did not receive the guideline-recommended PMRT. Only 6% of women with low risk disease received PMRT when it was not recommended. Unlike radiation after breast conserving surgery, there are no large published reports on the extent of appropriate or inappropriate use of radiation therapy among mastectomy patients to which these findings can be compared.
The only factor associated with underuse of PMRT was non-receipt of chemotherapy. Clinical factors such as tumor size and number of positive axillary nodes that influence the decision to treat with radiation are highly correlated with factors used to recommend chemotherapy. Therefore, it may be that non-receipt of chemotherapy in this group is a marker for patients who have elected to forego all curative treatment for their breast cancer, including PMRT.
Overuse of radiation therapy, i.e., use of PMRT among women for whom it is not recommended by the treatment guidelines in place at time of patient diagnosis, occurred in only 6% of women. Clinical, sociodemographic, and provider factors were all associated with PMRT use in this cohort. Younger women, and those with tumors that were larger, axillary lymph node-positive, estrogen receptor negative, or with non-ductal histology, were all more likely to receive PMRT. This suggests that physicians are basing recommendations for radiation on the perceived relative risk of recurrence for this cohort, despite the lack of evidence demonstrating its value. The presence of a gradient of odds ratios for the receipt of PMRT based on the precise number of positive axillary nodes (one versus two versus three) further supports the role of perceived risk in driving treatment recommendations in this cohort. It is important to note that the guidelines were revised in 6/2000 now recommending PMRT or the consideration of PMRT for all women with positive nodes regardless of age. Early breast reconstruction was independently associated with a lower likelihood of overuse in this group. This association may reflect concern that PMRT can lead to a less optimal cosmetic result after breast reconstruction.26
Education at the college level or above was associated with overuse of PMRT in this cohort suggesting that patients’ perceptions about risk and their preferences also may be contributing to the observed patterns of care. We also found evidence of institutional variability that persisted after controlling for tumor and patient-specific factors. This suggests that there is non-uniform acceptance of the evidence as synthesized in the NCCN guidelines, and a pattern of local, institution-specific biases in favor of more aggressive treatment as a result. That this practice occurs in the highly specialized centers that form the NCCN is consistent with Wennberg’s recent report on healthcare delivery (Dartmouth Atlas of Health Care project) showing that “patients served by even the best academic centers (teaching hospitals) experience unwarranted variations in health care”.7
Discretionary use of radiation therapy, or use of PMRT in women for whom the NCCN guidelines did not offer a definitive treatment recommendation, was also determined by clinical characteristics, and particularly by institution-specific patterns of care. Younger age, greater number of positive axillary nodes, close surgical margins, and receipt of chemotherapy were all associated with receiving radiation in this cohort. After accounting for these factors, we still found wide variability of PMRT use across NCCN institutions (p<.0001). We did not collect information from patients about their treatment preferences, however, it seems unlikely that the degree of variation we observed across this set of institutions could be explained wholly or even in large part by patient preferences. This raises the concern that treatment in this cohort of patients, for whom two medically acceptable options exist, may be driven by provider rather than patient preferences, a situation not consistent with the highest quality of care.7
Sadly, a randomized trial specifically addressing the benefit of PMRT in this group conducted by Southwest Oncology Group (SWOG S9927) closed due to poor accrual. This suggests that physicians’ beliefs about the value of PMRT may not only be driving patterns of use, but may also be serving as a barrier to research informing the optimal use of PMRT.
Our analysis has several limitations. We studied patterns of care in a selected group of cancer centers; the patients and providers in our sample likely differ from the general population, limiting the ability to generalize our findings. Distance from the nearest radiation facility has been shown to be an important predictor of radiation therapy after breast-conserving surgery,27,28
but we found no effect of travel distance, even though the median distance from the patient to the nearest radiation treatment facility in our study was similar. It is possible that patients in our centers are more motivated to seek treatment, and this motivation was sufficient to overcome the distance barrier.
We also recognize that our analysis is not a population-based study. However, there is no population-based data source that contains the information needed to appropriately control for the clinical factors that do and should drive decisions about radiation after mastectomy, such as margin status. Moreover, the demonstrated striking effect of inter-institutional variability which if present even among the NCCN centers, is likely to be present among institutions outside the NCCN as well.
Our study also has certain strengths. Unlike studies using administrative data with or without linkage to registry data, we had information about key variables such as education and travel distance at the level of the individual patient rather than at the aggregate level. This may explain why we were able to detect an effect of education as a significant, independent predictor of overuse of PMRT. More importantly, the availability of highly detailed clinical data in our study enabled us to fully account for the clinical factors that might drive treatment choice and to examine the effects of other patient characteristics and provider biases unconfounded by these factors.
In summary, we found that rates of concordance with definitive guidelines for PMRT were high. Appropriate use of PMRT among the high-risk cohort was the rule, while overuse of PMRT among women with low risk disease occurred infrequently. The only factor associated with underuse was non-receipt of chemotherapy, suggesting that care may appropriately reflect patient preferences. Although overuse was rare, it appeared to be driven by provider biases, and in particular, a tendency to treat women with higher risk disease more aggressively despite the absence of consensus opinion supporting this approach. Finally, we found considerable variability in the use of PMRT among women at moderate risk of recurrence, highlighting the need for focused clinical research in this group.
In its report “Ensuring Quality Cancer Care,” the National Cancer Policy Board5
recommended the use of radiation therapy following breast-conserving surgery as a good process indicator to study the quality of cancer care. Indeed, prior studies have largely focused on the use of radiation therapy after breast-conserving surgery as such a measure. Radiation therapy after mastectomy may also be an important quality indicator and national target for intervention, given its significant survival impact and the large number of lives at stake. The challenge will be to develop a quality monitoring system that includes sufficient clinical detail to identify women most likely to benefit from PMRT.