A single tumour can have many different genetic mutations at various locations, cancer researchers have found. In a study, two thirds of the specific genetic faults identified in tumours were not repeated in the same tumour.
'This adds another layer of complexity', said lead author Professor Charles Swanton, from Cancer Research UK's London Research Institute.
In what was the first genome-wide analysis of the genetic variations within one tumour, the British team studied the tumours of four kidney cancer patients treated at London's Royal Marsden Hospital. They took samples from various regions in both the advanced tumours in the kidneys, as well as from tumours in other organs after the cancer had spread.
'We used every possible genomics technique available. Even then we were only scratching the surface', Professor Swanton said.
Cancer drugs are often targeted at specific mutations of cancer cells identified via a biopsy, and often this analysis relies on a single biopsy.
The findings, published in the New England Journal of Medicine, underline the difficulty of treating cancer based on one biopsy. The team even found genetic signatures associated with both good and poor prognoses in different parts of the same tumour.
To understand the genetic diversity they saw, the researchers examined the evolutionary history of the mutations, a bit like a family tree. The results showed some common mutations in the 'trunk' of the tree that were present in a number of samples.
This emphasises the importance of early treatment – both in terms of targeting these common mutations and in diagnosing cancer before it spreads. Furthermore, the later the tumour cells are treated, the higher the chances that drug-resistant mutations could develop.