A new genetic test that tries to predict whether a woman with breast cancer will have a relapse won approval yesterday from the Food and Drug Administration, marking a step toward an era in which medical treatments are personalized for each patient. The approval was the first ever of such a complex genetic test, not only the first for breast cancer relapse. While other breast cancer recurrence predictive tests are being sold or developed, the new one, called MammaPrint, is the first to go through the formal F.D.A. approval process. The agency has signaled its intention to oversee more closely...