From Science:
In early 2007, a 28-year-old Japanese woman gave birth to a girl. Thirty-six days later, the mother was hospitalized with vaginal bleeding, which became uncontrollable. Doctors diagnosed leukemia, and she soon died. The baby developed normally until age 11 months, when a huge tumor appeared in her cheek. A biopsy determined the cancer was not sarcoma–a cancer of certain connective tissues–but a leukemic tumor somehow trapped in the child's cheek. The doctors alerted cell biologist Mel Greaves of the Institute of Cancer Research in Sutton Surrey, United Kingdom, who studies transmissible cancers. Scientists had suspected mother-to-fetus cancer in other cases with strong circumstantial evidence (especially with leukemia and melanoma, which both metastasize readily). But no one had done genetic tests to prove the cancer had grown from a single source and wasn't just an unfortunate coincidence.
In their investigation, Greaves and colleagues discovered incipient cancer cells in routine blood samples taken from the child at birth, strongly suggesting that the transmission happened in utero. They also examined a DNA sequence unique in each case of leukemia, the BCR-ABL1 sequence. It was identical in mother and daughter. Finally, tests showed the child's cancer cells were almost all maternal cells, with no genetic material from the father. This indicated that the transmission path was mother to fetus, not the reverse.
More here.
