微侵袭性（T1mi）乳腺癌的自然史不确定。本研究旨在评估在一项分数减量随机试验中，接受全乳腺放射治疗（WBI）的T1mi患者与T1a-2疾病患者进行保乳手术（BCS）后的局部和远处复发率，并进行长期观察。1234名T1-2 N0乳腺癌患者随机接受术后42.5Gy、16次或50Gy、25次分数剂量的WBI。进行了T1mi肿瘤与T1a-2疾病患者的比较分析。采用Kaplan-Meier估算法，比较局部复发（LR）、远处复发和总生存（OS），使用对数秩检验。平均随访时间为12年。其中3%（n = 38）的患者为T1mi肿瘤。 与T1a-2乳腺癌相比，10年LR率为22.6％，而T1a-2乳腺癌仅为6.9％（危险比（HR）= 3.73，95％置信区间（CI）：1.93, 7.19，p <0.001）。 T1mi肿瘤的10年远处复发风险为5.1％，T1a-2疾病为12.1％（HR = 0.56，95％CI：0.19,1.84；p = 0.36）。 T1mi的10年OS为91.5％，T1a-2疾病为84.4％（HR = 0.48，95％CI：0.18,1.30；p = 0.14）。无论是接受分数减量还是常规分数剂量治疗，LR的发生率并没有明显不同（HR = 1.21，95％CI：0.35,4.18；p = 0.77）。与T1a-2肿瘤相比，T1mi患者的LR风险明显更高，但OS仍然非常良好。未来的研究应评估更广泛的局部切除和加强放射治疗是否能够优化微侵袭性乳腺癌的局部控制。 版权所有 © 2023 The Authors. Elsevier Ltd.保留所有权利。

The natural history of microinvasive (T1mi) breast cancer is uncertain. The objective was to evaluate long-term local and distant recurrence rates following breast conserving surgery (BCS) in a prospective cohort of patients with T1mi compared to T1a-2 disease who received whole breast irradiation (WBI) in the context of a randomized trial of hypofractionation.1234 patients with T1-2 N0 breast cancer were randomized to receive adjuvant WBI of 42.5Gy in 16 daily fractions, or 50Gy in 25 daily fractions after BCS. An analysis of patients with T1mi tumors compared with T1a-2 disease was performed. Kaplan-Meier estimates of local recurrence (LR), distant recurrence, and overall survival (OS) were compared using the log-rank test.Median follow-up was 12 years. T1mi was found in 3% (n = 38) of patients. The 10-year LR rate was 22.6% in T1mi vs. 6.9% in T1a-2 breast cancer [hazard ratio (HR) = 3.73; 95% confidence interval (CI): 1.93, 7.19; p < 0.001]. The 10-year risk of distant recurrence was 5.1% for T1mi, and 12.1% for T1a-2 disease (HR = 0.56; 95% CI: 0.19, 1.84; p = 0.36). Ten-year OS was 91.5% in T1mi and 84.4% in T1a-2 disease, (HR = 0.48; 95% CI: 0.18, 1.30; p = 0.14). Rates of LR did not differ whether treated by hypofractionation or conventional fractionation (HR = 1.21; 95% CI: 0.35, 4.18; p = 0.77).The risk of LR was considerably higher in patients with T1mi compared to T1a-2 tumors, but OS remained very good. Future research should evaluate the utility of wider local excision and boost radiation to optimize local control for microinvasive breast cancer.Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.