Which of the following features is least associated with high-grade tumors?

High-grade tumors are typically characterized by features that indicate aggressive behavior and a tendency for rapid growth. One of the hallmark characteristics of these tumors is the presence of abundance of pleomorphic nuclei, which suggests significant cellular atypia and variation in cell size and shape. Similarly, necrosis is often observed in high-grade tumors due to inadequate blood supply caused by their rapid growth, leading to areas of dying tissue. High cellularity, another characteristic, represents a high number of cells in a relatively small area, typical of malignancies as they proliferate aggressively.

In contrast, low mitotic activity is not a feature associated with high-grade tumors. High-grade tumors are expected to show increased mitotic activity as they are actively dividing and displaying an aggressive growth pattern. Therefore, the presence of low mitotic activity would suggest a lower grade, indicating a slower-growing tumor that is more differentiated and less likely to metastasize. Hence, this choice reflects a characteristic that is least associated with the aggressive nature of high-grade tumors.