Unraveling mutagenic processes influencing the tumor mutational patterns of individuals with constitutional mismatch repair deficiency.

Summary: Imagine your body's DNA is an instruction manual. Sometimes, children are born with a broken "spell-checker" for their DNA, a rare condition called CMMRD. Because their cells can't fix DNA mistakes, these kids often get cancer at a very young age.

Scientists looked closely at 41 tumors from 17 of these patients to see exactly how their DNA was changing. They discovered that the mistakes in the DNA depend on three main things: which spell-checker gene is broken, the type of cancer, and even past cancer treatments! For example, a common cancer drug called temozolomide actually caused new types of DNA mistakes in later, secondary cancers. Understanding these unique DNA patterns helps doctors choose the best, safest treatments for these children in the future.