Sutro Biopharma is a clinical-stage oncology company developing antibody-drug conjugates (ADCs) — a class of cancer drug that links a targeted antibody with a cytotoxic payload to deliver chemotherapy directly to tumor cells. Sutro's core asset is its proprietary XpressCF® cell-free protein synthesis platform, which produces ADCs with payloads attached at precisely defined positions on the antibody (site-specific conjugation), unlike conventional ADC manufacturing which produces heterogeneous mixtures with variable payload placement. Sutro argues this homogeneous design improves both efficacy and tolerability. The platform also enables rapid screening of protein variants and supports dual-payload ADCs — attaching two distinct payloads to the same antibody. Sutro's lead program, STRO-004, is a tissue factor-targeting ADC that entered Phase 1 trials in November 2025, with initial data expected mid-2026. Preclinical programs include STRO-006 (targeting ITGB6 in lung and head and neck cancers) and STRO-227 (a dual-payload ADC targeting PTK7). Sutro has no approved products and generates revenue through licensing and collaboration deals with large pharma partners including Astellas, Merck, BMS, and Vaxcyte, earning upfront payments, milestones, and royalties. Sutro received roughly $1B in aggregate collaboration payments to date, and sold its royalty interest in Vaxcyte's pneumococcal vaccine candidates to Blackstone for $140M upfront in 2023. Sutro has reduced its workforce and moved manufacturing to contract manufacturers.