A new Ki-67 / E-cadherin cocktail reduces inter-observer variation of the calculated proliferative index

The proliferative index in breast carcinoma is usually calculated by the percentage of the Ki-67 positive cells out of the total number of malignant cells. In order to reduce the inter-observer variability of the calculated proliferative index a cocktail of antibodies against E-Cadherin and Ki-67 (Ki/Cad Cocktail) is presented. The cocktail was applied on 59 cases of infiltrating duct carcinoma of breast and compared to the consecutive slides stained for Ki-67 alone. The Ki/Cad cocktail has the advantage that by adding the anti E-Cadherin antibody, all the malignant epithelial cells are highlighted and can be differentiated from other proliferating cells. Statistical analysis proved that the cocktail increases the inter-observer agreement from 89 % to 97 % as compared to the Ki-67 alone and also reduces the overlap between the cancer grades.