MKI67 and breast cancer: Not only the clinical similarities including the spontaneous tumor incidence, onset age, course of the disease, and clinical-stage but also a number of molecular markers for human breast cancer such as BRCA gene mutations, EGF receptor (EGFR), Ki-67, human epidermal growth factor receptor (HER2)/neu, p53, p63, and matrix metalloproteinases were also demonstrated to serve an essential role in canine mammary tumors.