Beyond overall response rates, a critical area of excitement for new ADCs in lung cancer is their potential to treat brain metastases. Early data showing hints of intracranial efficacy is a significant point of interest, as this addresses a common and difficult-to-treat site of disease progression, offering a potential advantage over other therapies.

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.

The MFORTE trial revealed a significantly higher rate of brain-only progression in the lurbinectedin arm (27% vs 10%). This pattern suggests the drug's effective systemic control and lack of CNS penetration combine to unmask the brain as a primary sanctuary site for relapse over time.

The B7H3-targeted antibody-drug conjugate (ADC) ifanatumab deruxtecan shows a high intracranial response rate in SCLC, numerically even better than its systemic response rate. This suggests excellent CNS penetration, offering a promising strategy for managing brain metastases, a common and difficult challenge in SCLC.

Unlike novel challenges from bispecifics, upcoming SCLC therapies like antibody-drug conjugates (ADCs) and radiopharmaceuticals will benefit from existing familiarity. Community practices are already comfortable with these drug classes from their use in breast cancer (ADCs) and prostate cancer (radioligands), which should streamline their integration.

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.

Unlike the intact blood-brain barrier, the blood-tumor barrier within brain metastases is permeable. This "leakiness" allows large molecules like the ADC trastuzumab deruxtecan (TDXD) to enter and deliver its payload, providing a mechanism for its high CNS efficacy.

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.

While zongertinib demonstrates high systemic efficacy with a 77% response rate, its efficacy in the central nervous system (CNS) is significantly lower at 44%. This gap highlights a critical challenge for patients with brain metastases and underscores the need for combination therapies or next-generation drugs with better CNS penetration.