At the annual meeting of the American Association for Cancer Research in Chicago this week, one panel discussion focused on how genomics is helping cancer researchers figure out how cancer spreads. Harvard's Raghu Kalluri focused his talk on the stromal factors that determine the rate of a cancer's metastasis. For metastasis to take place, the tumor stroma — the 75 percent to 95 percent of a tumor's cells that act as the functional, supportive framework of a tumor but are not cancerous — need to be involved, Kalluri said.