In tumor staging, malignant cells that have metastasized to distant parts of the body are classified as stage:

In tumor staging, a classification of stage IV indicates that malignant cells have spread to distant parts of the body, which is known as metastasis. This stage signifies a more advanced level of cancer, where the disease has proliferated beyond the initial tumor site to other organs or tissues, making it more complex to treat.

Stage I typically refers to localized cancer that has not spread beyond its original site. Stage II usually involves a larger tumor size or nearby lymph node involvement but does not indicate distant spread. Stage III generally indicates more extensive regional spread, often to local lymph nodes but still does not involve distant metastasis. Therefore, stage IV is distinctly categorized for cases where the cancer has metastasized, confirming why this classification is aligned with cancer's most advanced and serious progression.