What kind of tumors are characterized by their ability to form secondary tumors?

Malignant tumors are characterized by their ability to invade nearby tissues and spread to other parts of the body, forming secondary tumors. This process, known as metastasis, allows malignant cells to detach from the primary tumor, travel through the bloodstream or lymphatic system, and establish new growths in distant organs or tissues. This invasive behavior is a key distinction from benign tumors, which do not spread and usually remain localized.

Fibrous tumors refer more specifically to a type of tumor composed mainly of fibrous or connective tissue, and while they can be benign or malignant, they do not inherently have the characteristic of spreading. Neoplasms is a broader term that refers to any abnormal growth of tissue, which includes both benign and malignant tumors. Therefore, the defining feature of malignant tumors in their ability to form secondary tumors makes them the correct choice in this context.