What does metastasis refer to in a medical context?

Metastasis specifically refers to the process by which cancer cells spread from the place where they first formed to other parts of the body. This occurs when cells break away from a tumor, travel through the bloodstream or lymphatic system, and form new tumors in other organs or tissues. Understanding this concept is crucial in the medical field, especially in oncology, as it affects treatment decisions and patient prognosis.

The other choices represent different medical concepts: the initial infection of a disease pertains to the beginning stage of an infectious process, the death of cells in the body can refer to necrosis or apoptosis but does not encapsulate the idea of spreading, and the body's immune response involves the mechanisms by which the immune system identifies and fights pathogens or abnormal cells, which is distinct from the spread of cancer.