Hypofractionated radiotherapy could provide more convenient treatment and had similar toxicities.However,reports of hypofractionated radiotherapy with two-stage expander/implant reconstruction are rare,Some studies have shown that hypofractionated radiotherapy had similar toxicities to conventional fractionated radiotherapy in patients with breast reconstruction. So,investigators conducted a phase II study to observe the reconstruction failure in hypofractionated radiotherapy with two-stage expander/implant reconstruction.

Results from a phase III randomized controlled study in China showed that Postmastectomy hypofractionated radiotherapy was non-inferior to and had similar toxicities to conventional fractionated radiotherapy in patients with high-risk breast cancer.However,reports of hypofractionated radiotherapy with two-stage expander/implant reconstruction are rare. Literatures report that reconstruction failure is a well-known complication of radiation therapy in breast cancer patients with reconstruction. Results may vary based on RT timing and technique. Some studies have shown that hypofractionated radiotherapy had similar reconstruction failure to conventional fractionated radiotherapy in patients with breast reconstruction. So,investigators conducted a phase II study to observe the reconstruction failure in hypofractionated radiotherapy with two-stage expander/implant reconstruction.

Inclusion Criteria:

• Pathologic diagnosis of stage I-IIIc invasive breast cancer (ductal, lobular, mammary, medullary, or ductal)

  ≤ T3 or N+

• negative surgery margins

• positive postoperative pathologic axillary lymph nodes after neoadjuvant chemotherapy (ypN+).

• Undergo mastectomy+expander+RT（hypofractionated radiotherapy）+delayed prosthesis reconstruction

• Sign the informed consent form

Exclusion Criteria:

• T4,
• axillary sentinel lymph node biopsy without axillary dissection
• Recurrent breast cancer or history of prior breast radiation therapy (neck, chest wall, axilla)
• Uncontrollable co-morbidities, including but not limited to active collagen vascular disease (e.g., systemic lupus erythematosus, scleroderma, or dermatomyositis), persistent or active infection, symptomatic congestive heart failure, unstable angina, mental illness incapacitating participation in this study
• Pregnancy or breastfeeding
• History of malignancy other than the following： (At least 5 years of tumor free survival with a very low risk of recurrence, e.g., carcinoma in situ of the cervix and basal cell or squamous cell carcinoma of the skin）
• requiring bilateral breast/chest wall radiation therapy