More than a dozen cancer types are increasing among people under 50, with some rising 6% annually. Health reporter Nina Agrawal explores what scientists are learning about environmental and lifestyle factors driving early-onset cancer, and how diagnoses upend young adults' careers, relationships, and family planning during critical life stages. Girls now menstruate earlier and have first pregnancies later than in the 1950s, expanding the vulnerable window where breast cells accumulate mutations that can lead to cancer.