Various patterns of Ki67 expression in BC.

<p>Ki67 grade I and Ki67/CK grade II in BC tissues (A, 200 ×); Ki67 grade II and Ki67/CK grade I in BC tissues (B, 200 ×); Ki67 is mainly expressed in cancer cell nucleus (C, yellow arrows, 200 ×), with few exceptions in stroma (C, red arrows), not in blood vessel (C, blue arrows); Ki67 expression levels are higher in invasive cancer nests (D, red ellipse, 200 ×) than carcinoma in situ (D, blue ellipse); for carcinoma in situ, Ki67 expression is more prominent at the tumor nest periphery than at the center (E, red arrows, 200 ×); for invasive carcinoma, haphazard Ki67 expression is observed in the disorganized tumor nests (F, red arrows, 200 ×); high Ki67 expression is observed at the tumor nests invasion edges both for carcinoma in situ with minimal invasion (G1, 200 ×; G2, 400 ×) and invasive ductal carcinoma (H1, 200 ×; H2, 400 ×); when a big tumor nest produces smaller seeding tumor nests, high Ki67 expression is observed at the conjunction between the two tumor nests (I1, 200 ×; I2, 400 ×). BC: breast cancer; CK: cytokeratin.