Which tumor feature is indicative of poor prognosis?

A high Ki-67 index is indicative of poor prognosis as it reflects an increased proliferation rate of tumor cells. Ki-67 is a nuclear protein expressed in actively dividing cells, and the index quantifies the percentage of tumor cells that are in the active phases of the cell cycle (excluding resting phases). A higher Ki-67 index indicates a more aggressive tumor behavior with a greater likelihood of rapid growth and metastasis, correlating with worse clinical outcomes.

In contrast, well-differentiated cells typically suggest a better prognosis, as they retain more of the characteristics of normal tissue and are less aggressive. Low mitotic activity also signifies a slower-growing tumor, indicating a potentially more favorable prognosis. The presence of lymphoid infiltrate can sometimes reflect an immune response to the tumor and does not always correlate with poor outcomes. Thus, a high Ki-67 index stands out as a reliable marker for poor prognosis due to its association with tumor aggressiveness and rapid cell proliferation.