When should women get screened for breast cancer? It’s a fraught question. Mammograms can yield false positives or detect lesions that pose no health threat, making patients anxious and exposing them to risks of follow-up tests. But not getting screened may risk missing the chance, however small, to catch a dangerous tumor early. Difficult decisions like this will become more common as medical tests and health information become unbound from the doctor’s office. Lab tests…