Unless a cell dies, it cannot serve a vital function to its host. Still, it is not the chromosome fusion that makes cells resistant, but the cells' genetic mechanisms, primal processes that drive them to survive at all costs. In acquired resistance, Bertino said, a cancer can be initially sensitive to a drug and be virtually eradicated, but a few cells remain and acquire resistance. They can do this most notably by quickly producing specific proteins, called efflux pumps, that thrust the drug out of the cell. But there are many, many other mechanisms of acquired resistance.
Intrinsic resistance is another story.
Cells throughout the body, particularly those in the liver and kidneys, are endowed with an ability to purge toxins. Liver and kidney cancer cells are among the most adept at resisting chemotherapy. And there is little wonder why this occurs, Bertino said. Many of the substances used to treat cancer are derived from natural products. With some of these substances, cells have had millions of years to figure out how to thwart them.