What Frei and Freireich discovered in the spinal fluid left them cold: leukemia cells were growing explosively in the spinal fluid by the millions, colonizing the brain. The headaches and the numbness were early signs of much more profound devastations to come. In the months that followed, one by one, all the children came back to the institute with a spectrum of neurological complaints—headaches, tinglings, abstract speckles of light—then slumped into coma. Bone marrow biopsies were clean. No cancer was found in the body. But the leukemia cells had invaded the nervous system, causing a quick,
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