A tumour can be a hotbed of diversity, British scientists have discovered. Just as different types of tumours have distinct genetic mutations, so do separate parts of the same tumour. Findings in a study published in the New England Journal of Medicine1 help to explain why cancer is so difficult to study and treat. A clinician's conclusion about prognosis or the best course of treatment can be contradictory depending on which part of the tumour the biopsy is taken from. “This adds another layer of complexity,” says Charles Swanton from Cancer Research UK’s London Research Institute, who led the study. “It makes flying to the Moon look like a walk in the park.”
As part of a clinical trial, Swanton’s team did a detailed analysis of the tumours of four patients with kidney cancer. They collected samples from several parts of the main tumours at various times during the trial, as well as from the organs to which the cancer had spread. Then every sample was analysed to look at its mutations, patterns of genetic activity, chromosome structure. “We used every possible genomics technique available. Even then we were only scratching the surface,” says Swanton. The team used its results to reconstruct the evolutionary history of each cancer. For example, the first patient’s tumour had split down two lines. One small part had double the usual tally of chromosomes and had seeded all the secondary tumours in the patient’s chest. The other branch had spawned the rest of the primary tumour’s mass. Similar results were seen in the other patients.