** Shares of drugmaker Biogen BIIB.O rise 5.3% to $209.69

** FDA approves a starting dose regimen for the under-the-skin injection of Eisai and Biogen's Alzheimer's drug Leqembi, allowing patients to begin treatment at home

** Previously, Leqembi was approved only with an intravenous starting dosage before patients could transition to other dosing options

** Leqembi is approved for early Alzheimer's disease, a memory-robbing brain disorder affecting more than 6.5 million Americans

** FDA says data showed the injection achieved drug exposure comparable to the intravenous regimen, supporting similar efficacy and safety

** FDA recommends genetic testing before treatment because certain patients face a higher risk of side effects

** Including session's moves, stock up ~18% YTD