Which of the following best describes a malignant tumor?

A malignant tumor is best described as invasive and potentially harmful. This is because malignant tumors have the ability to invade surrounding tissues and organs, which differentiates them from benign tumors that remain localized and do not spread. The invasive nature of malignant tumors allows them to penetrate and disrupt normal tissue function, leading to serious health consequences. Additionally, these tumors can metastasize, meaning they can spread to other parts of the body through the bloodstream or lymphatic system, further enhancing their potential to cause harm.

The other descriptors do not accurately capture the defining characteristics of malignant tumors. For instance, localized and non-invasive would apply more to benign tumors, which do not invade nearby tissues. Similarly, the characteristics of being encapsulated and solid are often associated with benign tumors, which are typically surrounded by a fibrous capsule that contains their growth. Lastly, stable and well-defined suggests a lack of growth and a predictable behavior, which is contrary to the aggressive nature of malignant tumors.