A leukemia therapy in which a patient's lymphocytes are genetically modified to attack the tumor cells causing the disease has shown dramatic effects in five patients, according to a new study.

The treatment appeared to eliminate cancer cells that had grown back after initially being beaten down by chemotherapy. Patients were then able to undergo bone marrow transplants, a grueling but sometimes curative procedure.

Might the "immunotherapy" have been curative on its own? That is the biggest of several unanswered questions.