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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.
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As multiple new drugs like antibody-drug conjugates (ADCs) become available for SCLC, the critical research question will shift from *if* they work to *when* they should be used. Future biomarker strategies must focus on optimizing treatment sequences, considering factors like the drug's target and payload.
Unlike many traditional chemotherapies, new antibody-drug conjugates (ADCs) like IDXD are demonstrating high objective response rates (over 45%) within the brain. This intracranial efficacy is a major advance for small cell lung cancer (SCLC) patients, who frequently develop hard-to-treat brain metastases, potentially reducing reliance on immediate whole-brain radiation.
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.
After standard immunotherapy biomarkers like PD-L1 and TMB proved ineffective in SCLC, the field shifted to a more direct approach. Novel therapies like the bispecific antibody tarlatumab target surface proteins such as DLL3, physically bridging immune cells to cancer cells without relying on predictive biomarkers.
The primary reason Antibody-Drug Conjugates (ADCs) stop working is payload resistance, a shift from the traditional belief that failure stems from tumors losing the target antigen. This insight drives development of multi-payload ADCs to overcome this resistance mechanism.
When sequencing antibody-drug conjugates (ADCs) for SCLC, resistance may be driven more by the cytotoxic payload (e.g., a topoisomerase 1 inhibitor) than the antibody's target antigen. This suggests prior exposure to a similar payload class could predict non-response, even when using an ADC with a different target.
Unlike older antibody-drug conjugates (ADCs), newer agents are designed so their chemotherapy payload can diffuse out of the target cell and kill nearby tumor cells that may not even express the target antigen. This "bystander effect" significantly enhances their anti-tumor activity.
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.
In notoriously hard-to-treat small cell lung cancer (SCLC), ADCs are emerging as a crucial next step. They hold promise for patients who progress after chemoimmunotherapy and newer targeted agents like tarlatamab, a setting where treatment options are currently scarce. ADCs could provide meaningful responses in this significant unmet need.
Nearly all promising antibody-drug conjugates (ADCs) in late-stage development for small cell lung cancer utilize a topoisomerase-1 (Topo-1) inhibitor payload. This overlap raises a critical clinical question: if a patient develops resistance to one ADC, will they respond to another? This creates a significant challenge for treatment sequencing and patient selection.