Cytosine, one of the four DNA bases, can be chemically modified by the addition of a molecule known as a methyl group to form 5-methylcytosine. This “epigenetic” modification has long been known to regulate gene expression and plays a critical role in processes like embryonic development. Its levels and distribution are also distinct in different tissues and are significantly altered in cancers. Analysing methylation patterns of DNA shed into blood and other bodily fluids by tumours can thus reveal both the presence and the location of a cancerous growth.
In 2019, Ludwig Oxford’s Dr Chunxiao Song and his team developed TET-assisted pyridine borane sequencing (TAPS) for mapping DNA methylation. The technology was spun out in 2020 to establish the biotechnology company Base Genomics, which was acquired for $410 million by Exact Sciences in October 2020. Compared to the previous gold standard for sequencing DNA methylation, TAPS is far more cost-effective and sensitive, and generates cleaner data to allow for additional genetic analysis.