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Ki-67 Proliferation Marker

Meaning

The Ki-67 Proliferation Marker is a nuclear and nucleolar protein expressed exclusively in the active phases of the cell cycle—G1, S, G2, and mitosis—but is completely absent in quiescent (G0) cells. Clinically, the immunohistochemical quantification of its expression, known as the Ki-67 labeling index, serves as a critical prognostic and predictive biomarker in the evaluation of various tumors, including those of endocrine origin. A high Ki-67 index signifies a high cellular proliferation rate, which is often correlated with more aggressive biological behavior and a poorer clinical prognosis, thus guiding therapeutic decisions and risk stratification.