Numbers: The Tricky Mutations in Cancer Cells

31: The percentage of genetic mutations shared by all the tumor samples taken from a patient with kidney cancer. Doctors often decide how to treat cancer by matching drugs to the mutations that appear in a single biopsy. But when Charles Swanton, an oncologist at the Cancer Research UK Foundation, took 12 biopsies from three of a kidney-cancer patient’s tumors, he found that only 40 of the 128 total mutations showed up in every sample. The other 88 mutations occurred in some tumor cells but not others. Swanton came up with similar results in three other patients, suggesting that optimum treatment for one region of a tumor might not be effective against another region. “Each biopsy tells a different story,” he says. “And that may be why cancer drugs do not work as well as we expect them to.”