All cells pick up oxygen and release waste into red blood cells that circulate in the bloodstream.
Cancer cells are no exception.
But as cancer cells multiply and form tumors, they can no longer survive by feeding on nutrients in nearby blood vessels alone. To sustain their rapid and deadly growth, cancer cells send out a chemical signal that causes blood vessels to develop and nourish the tumor. The blood vessels supply nutrients to the tumor which promote growth and metastasis. This unwelcome process is called angiogenesis. Without a source of nutrients, the starved tumor then shrinks.