Metastasis to internal breast lymph nodes Once breast cancer metastasis occurs, it will significantly affect the clinical stage, treatment plan, outcome and survival rate of patients. Statistics show that about 25% of breast cancer patients will develop internal breast lymph node metastasis, and early stage patients with breast cancer lesions located in the medial or central region of the breast are prone to develop internal breast lymph node metastasis. However, due to the hidden location of internal breast lymph nodes behind the sternum, biopsy is difficult and invasive, and the results of PET/CT and other imaging tests are not accurate, so there has been a lack of accurate and effective assessment and treatment tools. In the 1960s, doctors often adopted extended radical mastectomy (standard radical mastectomy for breast cancer + internal breast lymph node dissection including removal of 2 ribs), but this treatment method was largely abandoned from the 1980s because it was too invasive and had limited benefit to patients. Currently, the medical community generally adds radiation therapy to the internal mammary region after surgery for patients with pathologically confirmed or highly clinically suspicious internal mammary lymph node metastases, but it can easily lead to severe cardiac radiation injury. Many patients die years later not from the tumor, but from related cardiac complications. In the era of individualized tumor treatment, both “under-treatment” and “over-treatment” have to be opposed, therefore, the diagnosis and treatment of internal breast lymph node metastasis have been in an awkward situation. The new procedure integrates “diagnosis + treatment” into one. The reporter learned that the new “thoracoscopic endolymph node dissection” is a new procedure in which the entire endolymphatic drainage area of the breast is continuously excised using the thoracoscope immediately after the patient undergoes breast-conserving surgery or modified radical surgery for breast cancer. This procedure is a therapeutic minimally invasive surgery with the advantages of minimal trauma and quick recovery, and helps to clearly diagnose whether the internal breast lymph nodes have metastasized. If the presence of cancer metastasis in the internal breast lymph nodes is confirmed after cutting down, further radiotherapy damage to the heart can be avoided. The procedure also does not add additional physiological damage to the patient if no tumor metastasis is present. To date, more than 100 patients have successfully undergone this new procedure. Previously completed randomized studies have confirmed that there is no additional physiological damage to the patient as a result of the additional surgical procedure.