Most genetic testing of cancer cells focuses on individual point mutations, single spots in the genome where a base pair has changed, gone missing or been added. But these mutations don’t account for all cancers. There are many other structural variations in which large chunks of the chromosome undergo some kind of dramatic change and result in malignancies. “Now we realize that not just individual genes are important,” says Mikhail Kolmogorov, a scientist at the National Cancer Institute, “but.