Which cellular feature is an indicator of malignancy in tumor pathology?

Pleomorphism refers to the variability in the size and shape of cells and their nuclei within a tumor. This feature is significant in the assessment of malignancy because it indicates the loss of normal cellular differentiation and the presence of abnormal cellular characteristics. In malignant tumors, pleomorphic cells can often vary widely in appearance, which reflects aggressive growth and anaplasia, where cells lose the specific functions characteristic of their tissue of origin.

In contrast, uniformity of cells suggests a more organized structure typically seen in benign tumors, where cells retain their normal appearance. Hyperplasia involves an increase in the number of cells but does not necessarily indicate malignancy, as it can occur in non-cancerous conditions. Apoptosis, or programmed cell death, can occur in both benign and malignant processes and is not a reliable indicator of malignancy on its own. Thus, pleomorphism stands out as a critical feature that signals the presence of malignant tumors.