What does a higher Ki-67 index suggest about a tumor?

A higher Ki-67 index is indicative of a greater proportion of proliferating cells within a tumor. Ki-67 is a nuclear protein that is associated with cellular proliferation, and its expression levels are used as a marker to determine how quickly tumor cells are dividing. Tumors with a high Ki-67 index generally have a faster growth rate, which correlates with more aggressive behavior and a worse prognosis. This increased level of proliferation can suggest an underlying biology that is more likely to lead to metastasis and poorer outcomes, as aggressive tumors often have more rapid doubling times and are more likely to encroach on surrounding tissues or spread to distant sites. Therefore, the interpretation of a higher Ki-67 index aligns well with an understanding of tumor biology, emphasizing the aggressive nature of the tumor.