1.   It is thought to reflect defective cell proliferation control and delayed onset of normal differentiation.

2.   Earlier animal studies showed such donor cells could fuse with defective MD cells, possibly transferring a gene that MD patients lack.

3.   The defective cell and its offspring survive, living on to pick up the rest of the mutations necessary for cancer.

4.   But previously it was believed the cancer risk increased because the weakened immune system failed to destroy defective cells that could turn malignant.