MKI67 and breast cancer: Rodriguez-Martínez not only described the presence of exosomal miR-21 as being directly correlated with tumor size (p = 0.039), but also revealed that lower levels of this exosomal miRNA were found in breast cancer patients (37 out of 47 breast cancer patients) who were undergoing neoadjuvant chemotherapy compared to untreated patients that displayed exosomal miR-222 along with proliferation markers, such as ki67 (p = 0.05).