Cell division is an intricate chemical dance that's part individual, part community-driven. And in a neighborhood of 100 trillion cells, sometimes things go wrong. Maybe an individual cell’s set of instructions, or DNA, gets a typo, what we call a mutation. Most of the time, the cell senses mistakes and shuts itself down, or the system detects a troublemaker and eliminates it. But, enough mutations can bypass the fail-safes, driving the cell to divide recklessly. That one rogue cell becomes two, then four, then eight. At every stage, the incorrect instructions are passed along to the cells' offspring. Weeks, months, or years after that one rogue cell transformed, you might see your doctor about a lump in your breast. Difficulty going to the bathroom could reveal a problem in your intestine, prostate, or bladder. Or, a routine blood test might count too many white cells or elevated liver enzymes. Your doctor delivers the bad news: its cancer.