Early-onset malignancy under age 50 is increasing worldwide. In USA, Generation X and millennials are up to 2 times more likely to develop 17 of 34 common cancers than baby boomers at any given age. Globally, early-onset malignancy incidence rose 79.1% from 1990 to 2019. Early-life exposures link to early-onset malignancy development. Rising trends predict greater future cancer burden. Changes in early-life exposures mainly drive increases in younger generations' cancer rates. Paper discusses causes and prevention strategies for early-onset cancers.