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In 2012, a man in his 50s arrived at the Cleveland Clinic in Ohio with high-grade prostate cancer that had spread to a nearby lymph node. The treatment in such cases would ordinarily have been limited to drugs that block testosterone, a hormone that fuels prostate tumour growth. At the time, metastatic prostate cancer was considered uniformly fatal, and physicians were reluctant to subject someone to the side effects of surgery and radiation if these extra measures were unlikely to prolong life.