Shares of Agenus Inc., of Lexington, Mass., plummeted 23.5 percent on news that Glaxosmithkline plc’s Phase III DERMA trial testing its MAGE-A3 cancer immunotherapeutic, formulated with Agenus’s QS-21 Stimulon adjuvant, missed its primary endpoint. The trial failed to significantly extend disease-free survival in melanoma patients compared to placebo.