MKI67 and neoplasm: Generally, dormancy can be characterized as (i) cellular dormancy where tumor cells persist as either solitary cells that are non-proliferative (e.g., Ki67 or BrdU negative) and arrested in the G0 cell cycle phase, or (ii) tumor mass dormancy where the growth capacity of micrometastases is limited due to balanced proliferation and apoptosis, suppression of angiogenesis, or immune clearance (29–31).