What does the term "metastasis" refer to in the context of tumors?

The term "metastasis" specifically refers to the process by which cancer cells spread from the primary site of the tumor to distant organs or tissues in the body. This occurs when cancer cells invade surrounding tissues, enter the bloodstream or lymphatic system, and form new tumors in other locations. Metastatic tumors maintain the characteristics of the original cancer and can lead to significant complications and challenges in treatment, as they can affect multiple organs.

The other options do not accurately define metastasis. For example, the formation of a new tumor at the original site would pertain more to local recurrence rather than metastasis. Development of tumor resistance relates to how tumors may adapt to resist treatment, which is a different concept altogether. Similarly, shrinkage of the primary tumor describes a potential response to treatment rather than the spread of cancer cells. Therefore, the correct understanding of metastasis is crucial for comprehending cancer progression and management.