The archaeology of a tumour

By Joseph Milton, FT science intern

The successful mapping of two cancer genomes has enabled scientists to track the genetic evolution of skin and lung tumours for the first time, providing a catalogue of all the mutations invloved in the cancers. It has been hailed as a breakthrough which could revolutionise treatment and testing for these cancers.

The genomic maps of lung cancer and melanoma, a skin cancer, produced by researchers at the Wellcome Trust Sanger Institute in Cambridgeshire and published in Nature this week, track the DNA mutations that have accumulated in diseased cells through the course of the patients’ lives, revealing the histories of the cancers as they developed in the patients.

Mike Stratton, who led the melanoma study said: ”It’s like doing archaeological excavation. You’ve got traces and imprints of all these processes that have been operative for decades before the cancer arose.”

The researchers were able to trace the replication of every error found in the genome – from a healthy, pristine cell in the embryo, through naturally occurring mutations happening in the body during growth, to cancerous cells, severely damaged by cigarette smoke and ultraviolet light.

In the melanoma patient, tumour cells exposed to sunlight showed a very high proportion of a particular type of mutation, a kind of “signature” of UV damage. But as the cancer developed inside the patient’s body, shielded from exposure to sunlight, the proportion of these UV “signatures” started to decrease.

The scientists found more than 23,000 DNA mutations in the cancerous cells of a 55 year old smoker, and more than 33,000 in cells of a malignant melanoma sampled from a 45 year old man. Most of these mutations are harmless but occassionally a damaging mutation will occur in an important gene, leading to cancer.

The teams also found evidence of DNA repair mechanisms – cells fighting back against the cancer. They could tell this was taking place becuase many more mutations were seen in non-functional areas of DNA between genes than were found in active genes, suggesting that repair mechanisms prioritise important functional areas of DNA over non-functional regions.

The project has been lauded in the press, including in this paper, as the first time cancer genomes have been sequenced in full.

But this is not the first time that cancer development has been tracked by sequencing the genome, then looking at the progression and patterns of DNA mutations. In October Canadian scientists at the BC Cancer Research Centre, Vancouver, led by Samuel Aparicio, published a paper in Nature looking at the history of mutation in breast cancer genomes.

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