What is a primary method by which malignant tumors spread to distant body parts?

Metastasis is the primary method by which malignant tumors spread to distant body parts. This process involves cancer cells breaking away from the original (primary) tumor, traveling through the bloodstream or lymphatic system, and establishing new tumors (secondary tumors) in other organs or tissues. Understanding metastasis is crucial in oncology because it not only signifies a more advanced stage of cancer but also affects treatment decisions and prognosis.

In contrast, encapsulation typically refers to the formation of a fibrous capsule around a tumor, which is more characteristic of benign growths and does not facilitate the spread of malignant cells. Local invasion involves the direct infiltration of cancer cells into surrounding tissues, but this is a localized process and does not account for distant spread. Cellular differentiation pertains to how tumor cells resemble normal cells; while it is significant in understanding tumor behavior and aggressiveness, it is not a mechanism of spread itself.