blood spots
Written in blood?
Science Photo Library
CASEY LIM (not her real name) was 11 weeks pregnant when she gave a blood sample to test for
Down’s syndrome. It revealed multiple abnormalities in fragments of DNA circulating in her blood.
 Further analysis showed that the mutant DNA wasn’t from the fetus but from Lim’s own white blood
cells. A form of blood cancer called follicular lymphoma, which she had battled two-and-a-half years
 earlier, had stealthily returned.
Lim was one of the lucky ones. All too often, cancers are caught only after they have spread and
mutated into subtly different forms. This ability to evolve and resist our best treatments is what makes
cancer such a formidable foe. One way to root out its weaknesses is to repeatedly remove chunks of
tumour for analysis, but that is invasive and often risky.