The concept of Antibody-Drug Conjugates (ADCs) as simple "chemo attached to an antibody" is a significant oversimplification. True efficacy is highly dependent on complex factors like the linker's cleavage properties within the acidic tumor microenvironment, creating a "bystander effect" that is crucial to their function.

A key principle for managing ADC side effects is that the toxicity profile is largely determined by the linker-payload combination, not the antibody's target. For example, drugs with a deruxtecan payload will have similar GI toxicities regardless of the target, allowing clinicians to anticipate AEs across a class.

The varying outcomes of two similar Lilly ADCs (LY405/LY410) demonstrated that how a patient's body metabolizes the drug's payload is a critical factor. Absence of the CYP2D6 enzyme, crucial for a Topo-one payload, led to severe toxicity and death, highlighting a key variable beyond the linker and target.

Different TROP2-targeted ADCs using the same class of payload (topo-1 inhibitor) display distinct primary toxicities, such as diarrhea versus stomatitis. This highlights that subtle differences in drug-to-antibody ratio and linker technology create unique pharmacological profiles, making the drugs clinically distinct despite their apparent similarities.

When sequencing antibody-drug conjugates, clinical experience suggests that resistance to the chemotherapy payload is a primary driver of failure. Therefore, oncologists tend to avoid using another ADC with the same payload consecutively, preferring to switch both target and payload if possible.

Emerging data shows that a second ADC, particularly one with the same payload, often has limited efficacy. This suggests clinicians must be highly strategic in selecting the first ADC, as it may be their most impactful opportunity for this class of drugs.

A key principle for clinicians is that an antibody-drug conjugate's adverse events are primarily dictated by its linker-payload (e.g., deruxtecan, vedotin), not its specific antibody target. This allows for anticipating toxicities like neuropathy or GI issues based on the payload class, creating a predictable framework for management across different ADCs.

The differing efficacy and toxicity profiles of TROP2 ADCs like sacituzumab govitecan and Dato-DXD suggest that the drug's linker and payload metabolism are crucial determinants of clinical outcome. This indicates that focusing solely on the target antigen is an oversimplification of ADC design and performance.

Despite being "targeted therapies," multiple promising antibody-drug conjugates (ADCs) for small cell lung cancer (SCLC) show no correlation between the target protein's expression level and patient response. This suggests the payload or other factors are the primary drivers of efficacy, complicating biomarker development for patient selection.