2869 - Outcomes after Mutimodality Therapy for Clinically Internal Mammary Node Positive Breast Cancer: A Retrospective Cohort Study
Presenter(s)
X. Shen1, C. Zhang1, Y. Song1, H. Jing1, Y. Zhai2, W. Zhang3, Y. Tang4, H. Fang1, N. Lu1, Y. Song1, B. Chen5, and S. Wang1; 1Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, 2Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, 3State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, 4State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Beijing, China, 5Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, Beijing, China
Purpose/Objective(s): To assess outcomes and prognostic factors in breast cancer patients with clinically ipsilateral internal mammary lymph node involvement (cIMN+) treated with multimodality therapy.
Materials/Methods: We retrospectively analyzed 71 patients with cIMN+ breast cancer treated from June 2019 to December 2024 who received neoadjuvant chemotherapy (NAC), surgery, and postoperative radiotherapy to the breast/chest wall and regional lymph nodes. None of the patients underwent internal mammary lymph node dissection. An IMN boost was delivered using a simultaneous integrated boost (SIB) technique; the radiotherapy dose was individualized by the treating radiation oncologist. Acute and late radiation-related toxicities were graded according to CTCAE 5.0. Disease-free survival (DFS), overall survival (OS), distant metastasis–free survival (DMFS), locoregional recurrence–free survival (LRRFS), and internal mammary recurrence–free survival (IMRFS). Survival curves were estimated using the Kaplan–Meier method. Cox proportional hazards models were used for univariable and multivariable analyses of DFS.
Results: The median follow-up was 30.8 months. Only 1 patient (2.8%) developed internal mammary nodal recurrence. The median age was 48 years; 15.5% of patients had biopsy-confirmed IMN metastasis. After NAC, 43.7% achieved IMN clinical complete response (cCR). Conventional fractionation was used in 67.6% of patients. The median IMN boost EQD2 was 64 Gy (range, 50–73.04 Gy), and 63.4% received an IMN boost with EQD2 =64 Gy. The 5-year OS/DFS/DMFS/LRRFS/IMRFS rates were 84.6%/70.1%/70.3%/94.6%/98.2%, respectively. On multivariable analysis, non-breast pathological complete response (pCR) (hazard ratio [HR] 8.58, P=0.041) and triple-negative subtype (HR 3.89, P=0.026) were independently associated with inferior DFS. In an exploratory subgroup analysis, among patients not achieving IMN cCR, DFS did not differ significantly between IMN boost EQD2 =64 Gy and <64 Gy. Two patients (2.74%) developed grade 2 radiation pneumonitis, and one patient had elevated biomarkers of myocardial injury; no patient experienced grade =3 radiation-related toxicity.
Conclusion: In cIMN+ breast cancer treated with NAC, surgery, and postoperative radiotherapy, internal mammary and locoregional control were excellent in the absence of internal mammary lymph node dissection. Non-breast pCR and triple-negative subtype were key prognostic factors for DFS. Prospective studies are still needed to define the optimal radiotherapy dose–fractionation regimen for this patient population.