Tumours may have much greater genetic versatility than previously thought, and researchers say that might explain their ability to resist cancer treatments.
The finding comes from extensive and rigorous genetic sequencing carried out on a single tumour.
The human liver tumour that the scientists studied which was slightly more than 2.54 centimetres (1 inch) in diameter contained more than 100 million distinct mutations within the coding regions of its genes. That's thousands of times more than what scientists expected.
"With 100 million mutations, each capable of altering a protein in some way, there is a high probability that a significant minority of tumour cells will survive, even after aggressive treatment," study director Chung-I Wu, a professor of ecology and evolution at the University of Chicago, said in a university news release.
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The study was published in this week's issue of the Proceedings of the National Academy of Sciences.
The results suggest that even tiny tumours are likely to have extremely high genetic diversity, and to have cells that may be able to resist standard postsurgical chemotherapy and radiation, the researchers said.
"In a setting with so much diversity, those cells could multiply to form new tumours, which would be resistant to standard treatments," Wu explained.
Previous research has shown that cancer patients' chances of survival decrease as genetic diversity within tumours increases, because more mutations make drug resistance more likely.
"The possibility of high intra-tumour diversity even in small tumours suggests a need to re-evaluate treatment strategies," the study authors concluded.
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