Although researchers are trying to find universal markers to characterize each type of cancer, such as hormone receptors, HER2 and Ki67, inter-patient heterogeneity undermines current standards of practice with histological markers to accurately diagnose the grade of disease for all breast cancer patients (e.g., not equal levels of expression for a given marker between two patients where the underlying grade of their cancers is the same). The gene discussed is MKI67; the disease is cancer.