Scanning electron micrograph of dividing breast cancer cells

Breast-cancer cells — here shown dividing — may contain a multitude of chromosomal rearrangements. Credit: Cultura RM Exclusive/Rolf Ritter/Getty

Genomics

Tallying a cancer’s vast array of genetic changes

Advanced sequencing method yields a complex portrait of breast-cancer cell line.

Intensive sequencing of individual strands of DNA has revealed the scrambled genome of an important line of cancer cells.

Tumour genomes often include sections of chromosomes that are deleted, duplicated or fused together. To study one such unstable genome in detail, Michael Schatz at Johns Hopkins University in Baltimore, Maryland, and his colleagues used long-read sequencing to analyse the DNA of a breast-cancer cell line used often in research. The recently developed technique examines longer fragments of DNA than do older methods.

By combining long-read sequencing with RNA analysis, the team found several previously undiscovered regions in which two genes were fused together, as well as nearly 20,000 alterations in the genome’s structure. Many of these changes were missed by sequencing methods that analyse shorter fragments of DNA. The results suggest that efforts to sequence longer individual chunks of DNA may yield important information about cancer genome evolution.