Breast cancer seeds are characterized by the presence of breast cancer stem cells (BCSCs). But the cells are usually resistant to therapy and very easy to relapse. This innovation uses mammosphere forming units based on 0.5 cell/µl cell density, to measure BCSC’s tumor potential. This unit proves that the area of mammosphere cell that above 700 µm² can distinguish mammosphere cell that have the relapse potential with cells without such potential. Determination of this unit reflects the tumorigenic ability of breast cancer, so it can be used to predict the recurrence of the disease.