Cancer

At a cellular level, cancers are usually quite different from normal tissue. Many cancer cells actually change the chemicals on their surface, so are easy to identify. Most of the rest grow faster or change shape. And every cancer involves a genetic change that causes a difference in the chemicals inside the cell.

The immune system already takes advantage of surface markers to destroy cancer cells; however, this is not enough to keep us cancer-free. Nanobots will have several advantages. First, they can physically enter cells and scan the chemicals inside. Second, they can have onboard computers that allow them to do calculations not available to immune cells. Third, nanobots can be programmed and deployed after a cancer is diagnosed, whereas the immune system is always guessing about whether a cancer exists. Nanobots can scan each of the body's cells for cancerous tendencies, and subject any suspicious cells to careful analysis; if a cancer is detected, they can wipe it out quickly, using more focused and vigorous tactics than the immune system is designed for.