A significant factor that affects the value of the Ki-67 proliferation index (IK) is the interpretation and implementation approach. This method is based on visual or automated methods to count tumor nuclei labeled with Ki-67 antigen, and is prone to errors. Detection of Ki-67 is a useful tool in breast cancer and contributes to its molecular classification. The current study proposes a method for the quantification of Ki-67-positive tumor nuclei, which allows for the determination of the exact IK value that is required for tumor stratification based on the proliferation rate. The IK was assessed in 81 successive cases of diagnosed invasive ductal breast carcinoma using a semi-automated method that accurately identifies positive tumor cell nuclei. This method prevents the inclusion of other possible positive cells, including lymphoid, normal epithelia and hyperplastic. In small specimens with increased cell density, where the nucleus/cytoplasm ratio is markedly in favor of the nucleus and the distance between nuclei is small, the method allows precise quantification of the nuclei, even when the limits between nuclei are difficult to identify. In addition, images may be stored in a database, including the assessments, and easily accessed when required. We hypothesize that the semi-automated method for counting nuclei offers the most accurate method of assessing the IK and avoids counting errors that may occur through other methods.
Keywords: Ki-67 index; chemotherapy; counting method; invasive ductal carcinoma; luminal carcinoma.