Embryonic origin of cancer in newborn twins

Studying monozygotic twins who present with identical cancers informs on the developmental origins of childhood tumours. Here, we performed whole genome sequencing on multiple tumour, normal, and placental samples to reconstruct the phylogeny of a soft tissue cancer that spread in utero between monozygotic twins. This generalisable and scalable approach allows us to dissect the earliest stages of twinning, revealing unexpected asymmetrical contributions of embryonic lineages to the placenta and each twin.