MKI67 and breast carcinoma: Compared to those without myoepithelial differentiation, canine mammary carcinomas containing variable numbers of tumor cells with a myoepithelial differentiation (detected by immunostaining for SMA or p63) showed significantly lower Ki-67 proliferation indices, reduced infiltrative growths, lower rates of vascular or lymphatic invasion, and reduced metastatic spread to regional lymph nodes [33].