Breast Cancer

PV QA 4 - Poster Viewing Q&A 4

TU_1_3324 - The impact of postmastectomy radiation scar boost on local recurrence free survival in high risk patients

Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3

The impact of postmastectomy radiation scar boost on local recurrence free survival in high risk patients
A. A. Albert1, S. H. Mangana Jr2, L. Weatherall3, and S. Vijayakumar4; 1Department of Radiation Oncology, University of Mississippi Medical Center, Jackson, MS, 2University of Mississippi Medical Center, jackson, MS, 3University of Mississippi Medical Center, Jackson, MS, 4Radiation Oncology, University of Mississippi Medical Center, Jackson, MS

Purpose/Objective(s): A scar boost following postmastectomy radiation to a total dose of >50 Gy can be considered in cases of invasive breast cancer with high risk features such as advanced T stage, lymphovascular space invasion (LVSI), and positive margins. However the data supporting a chestwall scar boost are limited. The purpose of this study was to determine differences in 5-year local recurrence free survival (LRFS) based on the use of a chestwall scar boost.

Materials/Methods: We retrospectively analyzed 140 patients with invasive breast cancer treated with mastectomy and postmastectomy radiation at a single institution between 2007-2016. Patients received 50-50.4 Gy to the chestwall and the majority of scar boosts were 9-10 Gy. LRFS curves comparing patients treated with and without a scar boost were generated using the Kaplan-Meier method and compared via the log-rank test. Linear regression was used to determine factors associated with the use of a scar boost. Univariable and multivariable Cox regression was used to determine covariables associated with LRFS.

Results: 140 patients met inclusion criteria including 46 patients (32.9%) who did not receive a scar boost and 94 patients (67.1%) who did received a scar boost. The local recurrence rate for the entire cohort was 12% and the median follow up time was 48 months. Local recurrence rates were 10.5%, 8.3%, 13.7%, and 28.2% for Stage I, Stage II, Stage III, and Stage IV, respectively. Fifty-two percent of patients received neoadjuvant chemotherapy and 69.3% of patients received adjuvant chemotherapy. Patients with T4 disease were more likely to receive a scar boost (OR 3.57, 95% CI 1.22-10.4, p=0.02) compared to earlier stage disease. On subset analysis of patients with LVSI or positive margins, 5-yr LRFS was 80.6% in patients treated with scar boost compared to 71.4% in patients without a scar boost (p=0.233). In patients with T3 or T4 disease, 5-yr LRFS was 82.4% in those who received scar boost and 69.1% in patients who did not (p=0.943). Among patients with triple negative disease, 5-yr LRFS was 79.5% in patients that received a scar boost versus 60.0% in patients that did not (p=0.131). The use of a scar boost was not associated with a significant improvement in LRFS on Cox regression (HR 0.83, 95% CI 0.37-1.84, p=0.654).

Conclusion: Although the absolute percentage of local recurrences was higher among the high risk patients who did not receive a scar boost in addition to postmastectomy chestwall irradiation compared to the high risk patients who did, this did not translate into a statistically significant benefit with regards to local recurrence free survival. The majority of the patients received chemotherapy as a part of their treatment regimen suggesting that in the setting of modern systemic therapy, additional radiation in the form of a scar boost may not provide a significant local recurrence or overall survival benefit and can be omitted to avoid additional toxicity.

Author Disclosure: A.A. Albert: None. S.H. Mangana: None. L. Weatherall: None. S. Vijayakumar: None.

Ashley Albert, MD

Disclosure:
No relationships to disclose.

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