Abstract: Internal mammary lymph nodes (IMLN) constitutes approximately 25% of the lymph nodes of the breast. The status of IMLN is one of the prognostic factors in breast cancer patients and essential to regional staging and adjuvant treatment choice. Internal mammary-sentinel lymph node biopsy (IM-SLNB) is deemed a minimally invasive technique for the effective evaluation of IMLN status and useful in individualized diagnosis and treatment. Injecting radiotracer into glands around the areola through a modified injection technique and at increased injection dose results in the high identification rate of internal mammary sentinel lymph node (IMSLN). Thus, routine IM-SLNB is feasible in clinical practice. Internal mammary lymph drainage pattern is extensively studied, and the accuracy of IM-SLNB guided by modified injection technique is gaining preliminary validation. This review summarizes the progress in diagnosis and treatment of IMLN of breast cancer.