Until last week, leukemia survivor Fengfeng (not his real name) knew almost nothing about the person who saved his life 13 years ago. Holding a bouquet of flowers, Fengfeng spotted a woman in her 40s. He rushed to her and hugged her. He sensed this was the person he had been waiting for.

Thirteen years ago, Fengfeng was a 15-year-old middle school student in Chongqing. He was diagnosed with chronic myeloid leukemia, a type of cancer affecting the blood-forming cells of the bone marrow.

He has no siblings, and half-match transplant techniques using a patient's parent as the donor had not matured yet. So the only hope was to find a close match outside the immediate family, the possibility of which was only one in 100,000.