Nowadays, breast cancer is the leading oncological diagnosis in women worldwide. On the other hand, breast cancer treatment can be considered one of the most progressive therapeutic approach in the medical fi eld of oncology. The invasive types of breast cancer have a tendency to spread via lymphatic route, what brings in the issue of sentinel lymph node-the fi rst node into which the lymph drains from a given anatomical location. This review paper discusses the historical background of the concept of sentinel lymph node and focuses on clinical signifi cance of the positivity of sentinel lymph node(s) as well. Modern-day conservative therapeutic surgery of breast cancer should be in accordance with diagnostic and preventive interventions in the axilla, whose rate of invasiveness and morbidity must be also attenuated without worsening the patient´s prognosis and survival rate. Formerly, a complete axillary lymph node dissection was routinely performed for prophylactic and cancer staging purposes. The indiscriminate application of this approach was replaced by sentinel lymph node biopsy. Along with common histopathological examination, immunohistochemistry, as well as modern techniques of molecular biology are often employed. These state-of-the-art methods enabled the identifi cation of micrometastases, or even nanometastases, though their real prognostic value is yet to be concluded (Ref. 52).