Risk-Stratified Hypofractionated Radiotherapy After Breast-Conserving Surgery for Early Breast Cancer

Patients who undergo upfront breast-conserving surgery will be assigned to the high-risk group if any of the following high-risk factors are present:

• Age younger than 40 years.

  • Histology of invasive lobular carcinoma or micropapillary carcinoma.

    • Multifocal disease, defined as two or more breast tumor foci.

      • Tumor size greater than 3 cm.

        • Lymphovascular invasion.

          • Invasive carcinoma with an extensive intraductal component.

            • Estrogen receptor-negative disease.

Patients who receive neoadjuvant chemotherapy followed by breast-conserving surgery will be assigned to the high-risk group if any of the following high-risk factors are present:

• Age younger than 40 years.

  • Histology of invasive lobular carcinoma or micropapillary carcinoma.

    • Multifocal breast tumor before treatment.

      • Lymphovascular invasion.

        • Pathologic stage ypT1-2N0.

Patients who undergo upfront breast-conserving surgery will be assigned to the low-risk group if they meet either of the following criteria:

① Ductal carcinoma in situ (DCIS): age 40 years or older, unifocal disease on breast MRI, tumor size 3 cm or smaller, estrogen receptor-positive disease, and low-, intermediate-, or high-grade disease.

② Invasive carcinoma, including invasive ductal carcinoma, mucinous carcinoma, papillary carcinoma, or tubular carcinoma: age 40 years or older, unifocal disease on breast MRI, tumor size 3 cm or smaller, grade 1 to 3 disease, no lymphovascular invasion, and estrogen receptor-positive disease.

Patients who receive neoadjuvant chemotherapy followed by breast-conserving surgery will be assigned to the low-risk group if all of the following criteria are met: Age 40 years or older, unifocal disease on pretreatment breast MRI, pretreatment core needle biopsy showing invasive ductal carcinoma, and pathologic stage ypT0/isN0.