Final answer:
The term that means harmful, tending to spread, becoming progressively worse, and life-threatening is malignant.
Step-by-step explanation:
The correct term that means harmful, tending to spread, becoming progressively worse, and life-threatening is malignant. Malignant tumors are cancerous and can invade and damage neighboring tissues. Cells from malignant tumors can break away from the tumor and enter the bloodstream, leading to the formation of new tumors in other parts of the body.