Evaluating Omitting of Internal Mammary Irradiation Among Early Stage Intermediate Risk (N1) Breast Cancer

Inclusion Criteria:

* • Histologically confirmed invasive breast cancer

  * Underwent radical surgery with either mastectomy or breast conserving surgery and axillary lymph node dissection (ALND)
  * The number of positive lymph node should be 1-3 (N1).
  * Clinical high risk breast cancer (≥2 clinical risk factors)
  * Aged 18-80 years old
  * ECOG performance status ≤2 (Karnofsky ≥70%) Anticipative overall survival \>5 years Pathologically surgical margin \>2mm ER (estrogen-receptor), PR (progesterone-receptor), HER2 (human epidermal growth factor receptor 2) and Ki67 testing can be performed on the primary breast tumor Women of child-bearing potential must agree to use adequate contraception for up to 1 month before study treatment and the duration of study participation Ability to understand and willingness to participate the research and sign the consent form

Exclusion Criteria:

* • Axillary dissection of less than 10 lymph nodes

  * Pathologically positive ipsilateral supraclavicular lymph node
  * Pathologically or radiologically confirmed involvement of ipsilateral internal mammary lymph nodes
  * Pregnant or lactating women
  * Treated with breast reconstruction surgery
  * Severe non-neoplastic medical comorbidities
  * History of non-breast malignancy within 5 years with the exception of lobular carcinoma in situ, basal cell carcinoma of the skin, carcinoma in situ of skin and carcinoma in situ of the cervix
  * simultaneous contralateral breast cancer
  * Previous radiotherapy to the neck, chest and/or ipsilateral axillary region
  * Active collagen vascular disease
  * Definitive pathological or radiologic evidence of distant metastatic disease
  * Primary T4 tumor
  * Interval between radical surgery (mastectomy or breast conserving surgery) and radiotherapy was more than 12 weeks or interval between last dose of adjuvant chemotherapy and radiotherapy was more than 8 weeks