Roche, the world’s largest maker of cancer drugs, is spending $1.03 billion to buy a 56.3% stake in Cambridge, Mass.-based Foundation Medicine, a company that uses genetics to help select drugs for cancer patients. Roche, based in Basel, Switzerland, will also market Foundation’s diagnostic tests outside the U.S., help educate doctors as to the value of the tests in the U.S., and provide another $150 million to support additional research on Foundation’s products.