** Shares of drug developer OS Therapies rise 56.5% to $6.46 premarket

** Co says its experimental immunotherapy met the main goal of a mid-stage trial to treat a type of bone cancer

** Co says the therapy, OST-HER2, met the main goal of delaying the recurrence of the cancer by 12 months, compared to the historical comparable group

** Co says all patients who achieved the 12-month event-free survival goal are alive

** OST-HER2 was safe and well-tolerated in the study, OSTX says

** The therapy is being tested to prevent lung metastatic osteosarcoma, a type of recurrent bone cancer that has spread to the lungs

** Co says with these results, it is preparing to engage with U.S. FDA on "an accelerated pathway for approval"

** "We do not expect to have to treat additional patients as part of this process with FDA," OSTX adds

** Stock up 65.7% since its market debut in 2024

(Reporting by Sneha S K)

((Sneha.SK@thomsonreuters.com;))