In cancer, one particular type of body cell begins to grow and multiply abnormally, eventually forming a mass of renegade cells that doctors call a malignancy or a malignant tumor. Under a microscope, malignant cancer cells look different from their normal neighbor cells, and they act differently, too. They are aggressive and invasive; they don't respect the body's established boundaries between cells and tissues. Many of these malignant cells manufacture destructive chemicals called proteases that allow them to invade neighboring body areas. Others spread into the bloodstream and lymph ve…
