What is a sign that a tumor may be malignant?

Infiltration into surrounding tissues is indeed a strong sign that a tumor may be malignant. Malignant tumors are characterized by their aggressive nature, which often includes the ability to invade and infiltrate adjacent tissues. This invasive growth pattern can lead to the disruption of normal tissue architecture and function, making it a key indicator of malignancy. The presence of infiltrative borders is a critical factor that pathologists examine when assessing a tumor's behavior and potential for metastasis.

In contrast, slow growth rates and well-defined borders are typically associated with benign tumors. Benign tumors generally grow slowly and remain localized, without invading surrounding tissue. Additionally, while the presence of extensive necrosis may occur in both benign and malignant tumors, necrosis itself is not exclusively indicative of malignancy and can appear in various contexts, such as in rapidly growing benign tumors or non-neoplastic conditions. Therefore, the ability of a tumor to infiltrate surrounding tissues distinctly marks it as potentially malignant.