Cancer occurs as a result of mutations, or abnormal changes, in the genes responsible for regulating the growth of cells and keeping them healthy. The cells in our bodies replace themselves through an orderly process of cell growth: healthy new cells take over as old ones die out. Cell, in due course of time, gains the ability to keep dividing without control or order, producing more cells just like it and forming a tumor. The breast has developed from cells in the breast due to a malignant tumor. In this paper an attempt is made to find out the role of protein in reaching the different stages of breast cancer on the basis of experts opinion using the weighted multi expert neural networks system