CytomX Therapeutics is a clinical-stage oncology biotech built around its proprietary PROBODY platform, which uses peptide "masks" to block biologic cancer drugs from binding to healthy tissue. When a masked drug reaches a tumor, proteases in the tumor microenvironment cleave the mask off, activating the drug locally. The core commercial rationale is that many potent cancer drugs fail in practice not because they can't kill tumors, but because systemic toxicity limits the doses that can safely be given. CytomX has two programs in Phase 1: Varseta-M (CX-2051), a masked antibody-drug conjugate targeting EpCAM in colorectal cancer, and CX-801, a masked interferon alpha being developed in combination with Merck's KEYTRUDA in melanoma. Varseta-M is the lead program; Phase 1 data in late-line metastatic CRC showed confirmed response rates of 20–32% and disease control rates of 88%, comparing favorably to current late-line standard of care. CytomX plans to align with the FDA in 2026 on a registrational study design, with study initiation targeted for the first half of 2027. CytomX generates no product revenue and funds operations primarily by licensing the PROBODY platform to large pharma companies — past partners include BMS, Astellas, Amgen, Regeneron, and Moderna — through deals that include upfront payments, research funding, and milestones. Several older collaborations have wound down, reducing near-term licensing revenue, with Regeneron remaining the active partner.