The goal of this randomized Phase II clinical trial is to test the effects of omitting chest wall radiotherapy (RT) after prosthetic reconstruction in early-stage breast cancer patients. The main questions it aims to answer are:

• Can omitting chest wall RT after prosthetic reconstruction reduce the failure rate of breast reconstruction without significantly increasing the local recurrence rate?
• Does this approach ensure an improvement in the quality of life for patients without sacrificing therapeutic effectiveness?

Participants will:

• Be randomly assigned to one of two groups.
• One group will receive standard RT to the chest wall and supraclavicular and infraclavicular lymphatic drainage areas.
• The other group will have chest wall RT omitted and will only receive RT to the supraclavicular and infraclavicular lymphatic drainage areas.
• Participate in follow-up assessments to monitor reconstruction failure rates and local recurrence rates.

If there is a comparison group: Researchers will compare the outcomes of the two groups to evaluate the impact of chest wall RT omission on reconstruction failure and local recurrence risks.

Breast reconstruction, as part of the surgical treatment for breast cancer, offers an opportunity for patients who have undergone mastectomy to restore their body image and mental state, while post-mastectomy radiation therapy (PMRT) has advantages in local control and long-term survival of breast cancer. However, the integration of PMRT with reconstruction, especially using implants, raises concerns due to potential complications and the risk of reconstruction failure.

Reconstruction methods include autologous tissue and prosthetic implants, with the latter becoming more popular due to shorter surgery times and faster recovery. The choice between immediate, delayed, and two-stage reconstruction depends on tumor characteristics and patient factors. PMRT indications are based on tumor features and risks. The 2019 ESTRO expert consensus pointed out that the radiotherapy target area after breast prosthetic implantation should include the chest wall and all high-risk lymphatic drainage areas of the axillary region that have not been removed. While PMRT improves outcomes, it increases complications in implant-based reconstructions. Within two years after prosthetic reconstruction surgery, the proportion of patients who have at least one complication after radiotherapy is 39%, while it is 22% for patients who have not received radiotherapy. Early complications include fat or flap necrosis, thrombosis, infection, hematoma, delayed wound healing, and late complications include pain, prosthetic contracture, prosthetic exposure or rupture, and a decline in various indicators of aesthetic results. Patients who ultimately have to remove the implant or convert to autologous tissue reconstruction due to severe complications are defined as reconstruction failure. Among patients who received implant reconstruction and radiotherapy, the proportion of reconstruction failure after two years is the highest (18.7%); in contrast, the failure rate in the non-radiotherapy group or autologous reconstruction group is less than 5%.

Considering the high incidence of complications after prosthetic implantation, the failure rate of breast reconstruction may exceed 20%, while the local recurrence rate after breast reconstruction surgery is around 5%. For early-stage breast cancer patients undergoing cold knife one-step prosthetic reconstruction or two-step expander-prosthetic reconstruction, whether omitting chest wall radiotherapy can reduce the failure of reconstruction without significantly increasing the local recurrence rate, to ensure that improving the quality of life for patients does not sacrifice therapeutic effects. In response to this issue, this project proposes a "randomized Phase II clinical trial of omitting chest wall radiotherapy after prosthetic reconstruction in early-stage breast cancer" prospective study. This study will adopt a randomized controlled method, dividing patients into two groups, one group receiving routine chest wall plus supraclavicular and infraclavicular lymphatic drainage area radiotherapy, and the other group omitting chest wall radiotherapy and only receiving supraclavicular and infraclavicular lymphatic drainage area radiotherapy, aiming to evaluate the impact of omitting chest wall radiotherapy in PMRT after prosthetic reconstruction on the reconstruction failure rate of breast cancer patients, without significantly increasing the risk of local recurrence.

Inclusion Criteria:

• Undergoes prosthetic reconstruction (including cold knife one-step prosthetic reconstruction or two-step expander-prosthetic reconstruction.);
• Histologically confirmed invasive breast cancer patients with stage T1-2N1M0;
• ECOG score of 0-1;
• Indications for neoadjuvant therapy before surgery and adjuvant therapy after surgery.

Exclusion Criteria:

• Other metabolically active malignant tumors;
• Severe dysfunction of heart, lung, liver, kidney, or other vital organs;
• Uncontrolled diabetes or other endocrine diseases;
• Known allergy to radiotherapy or chemotherapy drugs;
• Pregnant or lactating women.

Open-label design, where the assessors are not blinded to the group allocation.