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Major complication Radiation therapyEquivalent Dose in 2 Gy fractions (EQD2; a/b ¼ 3.5) varied from 43.4 to 71.0 Gy (median dose: 48.6 Gy).Boost radiation therapy was administered to 49 patients. Major post-radiation therapy complications were observed in 24 (7.6%) patients. In multivariate analysis, an increasing EQD2 per Gy (odds ratio [OR]: 1.58, 95% confidence interval [CI]: 1.26e1.98; p < 0.001), current smoking status (OR: 25.48, 95% CI: 1.56 e415.65; p ¼ 0.023), and prosthetic breast reconstruction (OR: 9.28, 95% CI: 1.84e46.70; p ¼ 0.007) were independently associated with an increased risk of major complications. Conclusion:A dose-response relationship between radiation dose and the risk of complications was validated in this multi-center dataset. In this context, we hypothesize that the use of hypofractionated radiotherapy (40 Gy in 15 fractions) may improve breast reconstruction outcomes. Our multi-center prospective observational study (NCT03523078) is underway to further validate this hypothesis.

Purpose We conducted this study to investigate the prognosis and failure pattern after breast-conserving treatment (BCT) in patients with occult breast cancer (OBC) with negative breast magnetic resonance imaging (MRI) (MRI-OBC). Materials and methods Survival rates and failure patterns in 66 patients who received axillary lymph node dissection (ALND) and BCT for MRI-OBC between 2001 and 2013 at seven hospitals were analyzed. OBC was defined as adenocarcinoma in the axillary lymph node (ALN) +/− supraclavicular (SCN) or internal mammary lymph node (IMN) with a negative breast MRI. Results Fifty-four patients had only ALN metastasis (ALN only), and 12 patients had ALN metastasis along with SCN or IMN metastasis (ALN + SCN/IMN). Median follow-up was 82 months. The 5-year overall, disease-free, and breast cancer-free survival rates were 93.4%, 92.1%, and 96.8%, respectively. Nine patients experienced recurrence: breast (n = 4), regional lymph nodes (RLN, n = 1), distant metastases (DM, n = 2), breast/RLN (n = 1), and breast/RLN/DM (n = 1). Five-year disease-free survival was significantly higher in ALN only patients compared to ALN + SCN/IMN patients (96.1% vs. 75.0%; p = 0.02). Conclusions Patients with MRI-OBC were successfully treated with BCT. There was a small risk of ipsilateral breast cancer recurrence. Failure patterns depended on the extent of initial disease.