3004 - Comparison of Internal Mammary Irradiation vs. No Irradiation in Breast Cancer Patients Receiving Neoadjuvant Systemic Treatment: A Propensity Score Matching Study
Presenter(s)
A. Tinsurawattana, K. Thephamongkhol, J. Setakornnukul, and T. Jitwatcharakomol; Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
Purpose/Objective(s):
The role of internal mammary node irradiation following preoperative modern systemic therapy in breast cancer remains controversial. The advancements in systemic therapy, including chemotherapy and immunotherapy, may potentially obscure the postoperative irradiation benefit. This study aims to assess the value of internal mammary node irradiation (IMNI) in patients receiving postoperative radiotherapy after modern neoadjuvant systemic therapy.
Materials/Methods:
This was a single-center retrospective cohort study evaluating breast cancer patients who received neoadjuvant systemic therapy. Patients were divided into 2 groups: IMN-RT and non -IMN-RT. The criterion of the IMN-RT group was that 80% of the prescribed dose covered =98% of the Clinical Target Volume of IMN. The primary outcome was 5-year disease-free survival; the secondary outcomes were first recurrent events, 5-year overall survival, and cardiac toxicity.
Results:
From January 2012 to December 2021, 314 patients were evaluated (IMN-RT, 97 patients; non-IMN-RT, 217 patients). Due to differences in patient characteristics, propensity score matching was performed. This decreased the number of patients in each group to 93 patients. The median age was 53.1 years in both groups (p = 0.99). The majority of patients had T2 tumors (43% in the non-IMN-RT group vs. 42% in the IMN-RT group) and node-positive disease (81% vs. 85%, respectively). Extranodal extension was identified in 70% of patients in the non-IMN-RT group and 64% in the IMN-RT group. The majority of patients received radiotherapy using a three-dimensional (3D) technique. Regional lymphatic irradiation was administered to most patients covered supraclavicular area (94% in both groups) and whole axillary lymph node irradiation (80% in the non-IMN-RT and 85% in IMN-RT groups). In the IMN-RT group, 99.3% of the IMN clinical target volume (CTV_IMN) received at least 80% of the prescribed dose, compared to 60.9% in the non-IMN-RT group. Regarding the IMN planning target volume (PTV_IMN), 95.8% of the IMN-RT group received at least 80% of the prescribed dose, compared to 57.1% in the non-IMN-RT group. The median follow-up was 4.8 years. For the propensity score population, the 5-year DFS rates were as follows: IMN-RT, 63.2% (95% confidence interval [CI], 51.9%-72.5%), and non-IMN-RT, 72.1% (95% CI, 61.1%- 80.5%; P = .25). The groups’ 5-year overall survival did not differ; 68.6% (95% CI, 57.7%-77.2%) for IMN-RT and 79.1% (95% CI, 68.8%-86.4%; P = .11) for non-IMN-RT. For the whole cohort population, the most common first recurrent events in both groups are distant metastasis, 26.8% in IMN-RT and 17.97% in non-IMN RT. There was no significant difference in cardiac toxicity (IMN-RT, 2.1%; non-IMN-RT, 0.5%; P = 0.23).Conclusion:
In the modern upfront systemic therapy era, we could not find the benefit of internal mammary irradiation. However, due to its retrospective nature, prospective trials are necessary to address this scenario.