Final answer:
Metastasis is the process where cancer cells spread from the primary tumor to other parts of the body, forming new tumors called metastases. This is dangerous because it indicates advanced cancer, is difficult to control, and is responsible for most cancer deaths.
Step-by-step explanation:
When a cancer cell undergoes metastasis, it means that the cell has moved from the original (primary) tumor site to different parts of the body through the bloodstream. This process makes the disease particularly dangerous as it forms new tumors, known as metastases, which lead to further damage in other organs. As cancer cells possess the ability to continuously replicate and mutate, they propagate the disease throughout the body, seriously compromising the patient's health and making treatment more challenging.
Malignant tumors are a concern because of their potential to metastasize. Unlike benign tumors that remain localized, malignant ones can invade neighboring tissues and spread, indicating a poor prognosis for the patient. Therefore, metastatic cancer is often associated with most cancer deaths since it signals advanced disease and is harder to control or cure.