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Abstract
Purpose: To evaluate the role of postmastectomy radiation therapy (PMRT) in patients with node-negative breast cancer of 5cm or larger tumors undergoing mastectomy.

Materials and methods: Medical records of 274 patients from 18 institutions treated with mastectomy between January 2000 and December 2016 were retrospectively reviewed. Among these, 202 patients underwent PMRT, while 72 did not. Two hundred and forty-one patients (88.0%) received systemic chemotherapy, and 172 (62.8%) received hormonal therapy. Patients receiving PMRT were younger, more likely to have progesterone receptor-positive tumors, and received adjuvant chemotherapy more frequently compared with those without PMRT (p <0.001, 0.018, and <0.001, respectively). Other characteristics were not significantly different between the two groups.

Results: With a median follow-up of 95 months (range, 1-249), there were 9 locoregional recurrences, and 20 distant metastases. The 8-year locoregional recurrence-free survival rates were 98.0% with PMRT and 91.3% without PMRT (p=0.133), and the 8-year disease-free survival (DFS) rates were 91.8% with PMRT and 73.9% without PMRT (p=0.008). On multivariate analysis incorporating age, histologic grade, lymphovascular invasion, hormonal therapy, chemotherapy, and PMRT, the absence of lymphovascular invasion and the receipt of PMRT were associated with improved DFS (p=0.025 and 0.009, respectively).

Conclusion: Locoregional recurrence rate was very low in node-negative breast cancer of 5cm or larger tumors treated with mastectomy regardless of the receipt of PMRT. However, PMRT was significantly associated with improved DFS. Further investigation is needed to confirm these findings.

Affiliations

Kyubo Kim  1 , Jinhong Jung  2 , Haeyoung Kim  3 , Wonguen Jung  1 , Kyung Hwan Shin  4 , Ji Hyun Chang  4 , Su Ssan Kim  2 , Won Park  3 , Jee Suk Chang  5 , Yong Bae Kim  5 , Sung Ja Ahn  6 , Ik Jae Lee  7 , Jong Hoon Lee  8 , Hae Jin Park  9 , Jihye Cha  10 , Juree Kim  11 , Jin Hwa Choi  12 , Taeryool Koo  13 , Jeanny Kwon  14 , Jin Hee Kim  15 , Mi Young Kim  16 , Shin-Hyung Park  17 , Yeon-Joo Kim  18
1 Department of Radiation Oncology, Ewha Womans University College of Medicine, Seoul, Korea.
2 Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
3 Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
4 Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea.
5 Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea.
6 Department of Radiation Oncology, Chonnam National University Medical School, Gwangju, Korea.
7 Department of Radiation Oncology, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
8 Department of Radiation Oncology, St. Vincent's Hospital, College of Medicine, The Catholic University of Korea, Suwon, Korea.
9 Department of Radiation Oncology, Hanyang University College of Medicine, Seoul, Korea.
10 Department of Radiation Oncology, Yonsei University Wonju College of Medicine, Wonju, Korea.
11 Department of Radiation Oncology, Cheil General Hospital and Women's Healthcare Center, Seoul, Korea.
12 Department of Radiology, Chung-Ang University College of Medicine, Seoul, Korea.
13 Department of Radiation Oncology, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.
14 Department of Radiation Oncology, Chungnam National University School of Medicine, Daejeon, Korea.
15 Department of Radiation Oncology, Keimyung University School of Medicine, Daegu, Korea.
16 Department of Radiation Oncology, Kyungpook National University Chilgok Hospital, Daegu, Korea.
17 Department of Radiation Oncology, Kyungpook National University Hospital, Daegu, Korea.
18 Proton Therapy Center, National Cancer Center, Goyang, Korea.