Theseus Pharmaceuticals Inc., a startup developing new tyrosine kinase inhibitors to overcome treatment-resistant cancer mutations, has raised $100 million in a series B financing led by Foresite Capital. Co-founded at the health care investment firm Orbimed with former Ariad Pharmaceuticals Inc. scientists who pioneered the development of pan-variant kinase inhibitors, the company's lead candidate is THE-630, a next-generation pan-variant KIT inhibitor for the potential treatment of refractory gastrointestinal stromal tumors.