Material Event (Form 8-K)

On August 13, 2025, CytomX Therapeutics, Inc. (the "Company") announced an update on the CX-2051Phase 1 study. The CX-2051dose expansions at 7.2 mg/kg, 8.6 mg/kg, and 10 mg/kg doses, administered every three weeks, have each enrolled approximately 20 patients as planned. A single Grade 5 treatment-related acute kidney injury occurred in a patient with a complex medical history, including having a solitary kidney. The Grade 5 event was believed to be secondary to nausea, vomiting and diarrhea. The Company was made aware of the event on July 11, 2025 and promptly reported the event to the FDA on July 18, 2025 in accordance with regulatory requirements. The CTMX-2051-101Safety Review Committee convened on July 14, 2025 and supported continued study execution and enrollment. The CTMX-2051-101study is ongoing, with a Phase 1 data update expected by Q1 2026.