What defines a malignant tumor in general?

A malignant tumor is characterized primarily by its ability to invade surrounding tissues. This invasive behavior is a fundamental property of malignancy and distinguishes malignant tumors from benign tumors. Benign tumors may grow larger but typically remain localized and do not spread to other parts of the body. In contrast, malignant tumors can infiltrate nearby tissues, disrupt normal cell function, and potentially metastasize to distant sites through the lymphatic system or bloodstream. The invasive nature of malignant tumors is closely linked to their aggressive growth patterns and ability to cause harm to neighboring structures, which is why this characteristic is used to define them in a clinical context.