The mysterious giant chromosomes found in some cancers are formed when DNA shatters and recombines.

Neochromosomes are made up of pieces of the 46 chromosomes that each human cell normally carries. To study how they form, a team led by Anthony Papenfuss at the Walter and Eliza Hall Institute of Medical Research in Melbourne and David Thomas of the Garvan Institute of Medical Research in Sydney, both in Australia, sequenced the DNA of neochromosomes isolated from liposarcomas.

They used a mathematical model to show that certain cancer genes can drive normal chromosomes — in particular chromosome 12 — to break into pieces and reform as circles. The circles, which carry cancer genes, grow in size as certain genes become amplified, and eventually split to form giant linear chromosomes.

A drug targeting genes that drive this process could kill the cancer cells, the team proposes.

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