Antibody-Drug Conjugates in Oncology: Principles, Clinical Development, and Future Directions.

Antibody-drug conjugates (ADCs) have emerged as a major therapeutic modality in oncology, enabling the targeted delivery of highly potent cytotoxic agents while expanding the therapeutic window in solid tumors. Recent clinical successes across breast, lung, and genitourinary cancers have highlighted that ADC efficacy is governed not only by target expression, but also by the integrated optimization of antibody engineering, linker chemistry, payload selection, and tumor-specific biology. In this review, we summarize the fundamental principles underpinning ADC design, including antibody format and Fc engineering, linker stability, payload classes, drug-to-antibody ratio optimization, and the bystander effect. We then discuss tumor antigen biology and target landscapes across solid tumors, with particular emphasis on how antigen density, heterogeneity, internalization kinetics, and intracellular trafficking shape clinical activity. Uro-oncological malignancies-especially urothelial carcinoma-are presented as a clinically advanced and instructive paradigm for ADC development. Experience from these tumors illustrates both the opportunities and limitations of ADC therapy, including mechanisms of response and resistance, biomarker-driven patient selection, rational combination strategies, and safety management in real-world practice. Finally, we provide a forward-looking perspective on next-generation ADC development, highlighting emerging conjugation technologies, bispecific and conditionally activated ADCs, strategies to overcome resistance, and evolving clinical trial designs. By integrating engineering principles with tumor biology and clinical execution, this review aims to offer a translational framework to guide the future development and implementation of ADCs across oncology.