In December 2005, a series of mysterious symptoms — night sweats, easy bruising, swollen ankles and breathlessness upon exertion — prompted Barry to see his doctor. Only six months earlier, a physical exam had found nothing abnormal. But now Barry’s white blood cell count was through the roof.

A bone marrow test the next day revealed a genetic abnormality called the Philadelphia chromosome that is the signature of chronic myelogenous leukemia, or C.M.L., a blood cell cancer that in the last decade has been transformed from ultimately fatal to nearly always treatable, usually until something else claims the patient’s life.