L. L. Frasier5, S. E. Holden5, T. R. Holden6, J. R. Schumacher5, G. Leverson5, B. M. Anderson8, C. C. Greenberg5, H. B. Neuman5,7 8University Of Wisconsin,Department Of Human Oncology,Madison, WI, USA 5University Of Wisconsin,Wisconsin Surgical Outcomes Research Program, Department Of Surgery,Madison, WI, USA 6University Of Wisconsin,Department Of Medicine,Madison, WI, USA 7University Of Wisconsin,Carbone Cancer Center,Madison, WI, USA
Introduction: In the past decade, there is new evidence that patients receiving post-mastectomy radiation therapy (PMRT) experience reduced recurrence and an absolute survival benefit, strengthening consideration in patients with risk profiles for which PMRT has not previously been recommended. However, the actual impact of these data on practice has not been examined. We sought to investigate changes in rates of PMRT over time according to risk of recurrence.
Methods: Female patients with stage I‑III breast cancer who underwent mastectomy from 2000-2011 were identified in the SEER database (n=62,442). Temporal trends in the proportion of patients receiving PMRT were investigated, grouping patients by tumor characteristics associated with prognosis (tumor ≤ vs. > 5 cm; 0, 1‑3, or 4 or more lymph nodes). Joinpoint regression fits a series of joined straight lines together to determine whether there is a statistically significant change in the slope of the line(s) at any given point. We used this to analyze trends of PRMT use over time. Results are further summarized as annual percentage change (APC), or the slope of the line segment.
Results: The highest receipt of PMRT (initially 62%) was seen in patients at highest risk of recurrence, those with four or more positive lymph nodes (any tumor size) and patients with >5 cm tumors and 1-3 positive lymph nodes. For this group of patients, receipt of PMRT was increasing by 0.8% per year and stable over the study period (no change in slope was identified). PMRT receipt was lowest (initially 7.5%) for patients with tumors ≤5 cm and no positive lymph nodes, and increased by 2.6% per year (no change in slope). In contrast, the cohort of patients with tumors ≤5 cm and 1-3 positive lymph nodes, had a baseline receipt of PMRT of 26.9%, and did not change from 2000- 2006, after which change of slope was identified (p=0.0189). Thereafter, the APC increased to 9.0% for the remainder of the study period (2007-2011).
Conclusion: Since 2000, the use of PMRT has slowly but steadily increased over time for breast cancer patients across risk strata. However, there was a significant acceleration in the increased uptake of PMRT for patients with tumors ≤5 cm and 1-3 positive lymph nodes after 2007, likely representing change in practice patterns related to a broadening of the indications for PMRT in response to new evidence of a survival advantage. It will be important to monitor the magnitude of benefit from PMRT in current everyday practice to ensure the improvements in disease free survival and overall survival persist and that the benefits of this treatment outweigh the risks.
