HER2-directed TKIs (like zongertinib) and ADCs (trastuzumab-deruxtecan/TDXD) have different mechanisms, and clinical data shows they are effective when used sequentially. Zongertinib works post-TDXD, and vice-versa. However, there is no evidence to support using one HER2 TKI after another has failed.

Historically, HER2-mutated lung cancer was treated with cytotoxic chemotherapy, unlike other oncogene-driven cancers that used targeted therapies upfront. Zongertinib's approval as a first-line oral TKI marks a significant philosophical shift, aligning its treatment strategy with the biomarker-driven care standard in lung oncology.

Despite both being options, experts favor the TKI zongertinib for second-line treatment of HER2-mutant NSCLC. This preference is driven by zongertinib's higher response rates (~71%) and longer progression-free survival in this setting, coupled with a better side effect profile compared to the ADC trastuzumab-deruxtecan (TDXD).

The specific type of HER2 mutation significantly impacts TKI efficacy. YVMA exon 20 insertions show the highest response rates. Other TKD (tyrosine kinase domain) mutations perform moderately well, while non-TKD mutations respond poorly. This molecular nuance is critical for predicting treatment success and managing patient expectations.

Even if randomized trials show zongertinib's efficacy is merely comparable to chemoimmunotherapy, its significantly milder safety profile—especially its lack of cardiac toxicity and manageable side effects—is expected to make it the preferred first-line choice. Patient quality of life and tolerability are becoming decisive factors in treatment selection.

For HER2-mutant NSCLC, Zongertinib (a TKI) is now the first-line choice. While TKIs show activity after ADCs like TDXD, the effectiveness of using an ADC after TKI failure remains an unproven but critical clinical question for oncologists.

The new treatment paradigm for HER2-positive lung cancer will likely involve sequencing a TKI like zongertinib first, followed by an antibody-drug conjugate (ADC). Early data suggests that the efficacy of TKIs is significantly reduced when used after an ADC, making the TKI-first approach critical for maximizing patient outcomes.

Zongertinib shows a meaningful intracranial response rate of ~44% in HER2-mutant NSCLC. This efficacy supports initiating systemic TKI therapy for patients with small, asymptomatic brain metastases and monitoring closely with short-interval scans, potentially avoiding or delaying brain radiation and its associated toxicities.

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.