What Is an Antibody–Drug Conjugate (ADC)? Mechanism, FDA-Approved Drugs and Implications for Patients

Why Are ADCs in the Spotlight?

Conventional chemotherapy works but often harms healthy tissue. Antibody–Drug Conjugates (ADC; Antibody-Drug Conjugate)combine a cancer antigen-recognizing monoclonal antibodywith a potent cytotoxic payload and a carrier linker , providing “precise intracellular delivery.” Systemic toxicity may fall while efficacy is maintained. Success still depends on choosing the right target antigen , appropriate linker stability and patient selection , among other design and clinical factors.

• Greater efficacy: Highly potent chemotherapy reaches the tumor.
• Greater selectivity: Antigen targeting relatively spares healthy tissue.
• New indications: More options, particularly for recurrent/resistant disease.

ADC Structure and How It Works

1. Antibody (mAb): Recognizes and binds the tumor-specific antigen.
2. Linker: Stable in circulation, breaks down inside cells to release the payload.
3. Payload: Generally topoisomerase I inhibitors (e.g., deruxtecan) or microtubule inhibitors (e.g., MMAE), highly potent agents.

In some ADCs, payload escaping the cell may also affect neighboring cancer cells through the bystander effect .

Important Clinical Notes

• Biomarker: Target antigen expression (e.g., HER2, TROP2, c-MET, TF, FRα) is critical for selection.
• Safety: Closely monitor class-specific toxicities, e.g., ILD/pneumonitis, ocular toxicity and peripheral neuropathy.
• Combinations: ADC + immunotherapy/chemotherapy may become new standards.

FDA-Approved ADCs (Chronological)

*Gemtuzumab ozogamicin was approved in 2000, withdrawn in 2010 and reapproved in 2017. †Moxetumomab pasudotox was approved in 2018 and permanently withdrawn from the US market in 2023 by its manufacturer.

ADCs for Patients: 6 Frequently Asked Questions

1. How Do ADCs Differ from Chemotherapy? An antibody delivers chemotherapy directly to tumors, potentially reducing healthy tissue exposure.
2. Suitable for Everyone? No. Tumor antigen (e.g., HER2, TROP2, c-MET, FRα) and previous treatments are assessed.
3. Do Adverse Effects Disappear? No. Serious class effects, e.g., ILD/pneumonitis, ocular toxicity and neuropathy, may occur; close monitoring is essential.
4. When Are They Considered? Usually for advanced, recurrent/resistant disease; some 1st-line combinations are standard, e.g., enfortumab + pembrolizumab in urothelial cancer.
5. What Does “Tumor-Agnostic” Mean? HER2-positive (IHC 3+) or another specified target biomarker allows approval regardless of the primary organ (e.g., T-DXd).
6. Access in Turkey? Licensing/reimbursement vary by indication and require individual assessment.

Brief Comparison: Payload and Target Examples

Where Are We Heading?

• Tumor-agnostic expansion: The approach initiated with T-DXd is being investigated for other targets, e.g., TROP2.
• Combination strategies: ADCs + immunotherapy/chemotherapy may establish durable earlier-line roles, e.g., EV + pembrolizumab.
• New targets and bispecific ADCs: Platforms such as c-MET, HER3 and EGFR-HER3.
• Safety optimization: Linker innovation, payload selection and dose intensity to manage ILD/ocular/neuropathy risks.

Summary

ADCs are the most mature clinical examples of target-directed chemotherapy delivery in cancer care. Approved from the early 2010s, these agents opened many standard treatment settings in the 2020s for breast, lung, ovarian, urothelial and hematologic cancers. Matching patients and targets correctly and managing toxicity remain critical. The 2024 HER2 tumor-agnostic approval and 2025 TROP2 expansions suggest an increasingly central future role.