MKI67 and breast cancer: Like ALDHhi tumors, Ep-CAMhi/ALDH1hi breast cancers significantly correlated with markers of higher proliferation, including Ki-67 positivity status, combined loss of p21/p27 (p = 0.002) (Table 2A), and larger tumor size (p = 0.019) (Table 2B) in addition to ER negative status (p = 0.015).