The introduction of fine needle aspiration biopsy (FNAB) into diagnostics set new standards for less invasive morphological diagnostics research. This diagnostic method is better in many ways than core biopsy. In some researchers' view, FNAB is not an infallible method for assessing breast lesions, because it requires highly trained radiologists and cytologists in order to correlate the cytological findings with a radiological examination. Some researchers argue that FNAB is characterized by high diagnostic sensitivity and specificity; others that it has a greater advantage when it comes to costs in relation to conventional lymph node biopsy. Using ultrasound to guide FNAB decreases the number of false negative results and increases the sensitivity and specificity of FNAB. Fine needle aspiration biopsy plays an important role in the initial determination of the staging of breast lesions and of the character of the lesions (benign or malignant).