Merck announced that the FDA has issued a complete response letter regarding its New Drug Application (NDA) for ridaforolimus, an investigational medicine under development for maintenance therapy in patients with metastatic soft tissue or bone sarcoma who have stable disease or better after four or more cycles of chemotherapy.

The complete response letter states that FDA cannot approve the application in its present form, and that additional clinical trial(s) would need to be conducted to further assess safety and efficacy.

Ridaforolimus is an investigational small-molecule inhibitor of the protein mTOR, a protein that acts as a central regulator of protein synthesis, cell proliferation, cell cycle progression and cell survival, integrating signals from proteins known to be important to malignancy. Dysregulation of mTOR leads to altered signaling pathways in certain cancers, like sarcomas.

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