CytomX Therapeutics won FDA fast track designation for varsetatug masetecan (CX-2051), an EpCAM-directed masked antibody-drug conjugate for relapsed/refractory metastatic colorectal cancer. The designation was supported by phase 1 dose-expansion data from CTMX-2051-101, including an objective response rate that rose with higher expansion doses. Across evaluated expansion cohorts, confirmed objective response rates were reported at 6% (7.2 mg/kg), 20% (8.6 mg/kg), and 32% (10 mg/kg). The company also reported median progression-free survival estimates of 5.5 to 7.1 months depending on the dose level, with disease control rates around the high-80% range. CytomX said it is targeting a potential monotherapy registrational approach in the first half of 2027, with diarrhea flagged as the most common treatment-related adverse event, including grade 3 events under an updated prophylactic regimen.