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.

Despite both Zongertinib and Sevabirtinib showing high efficacy in HER2-mutant NSCLC, Zongertinib's selective nature results in a much better safety profile. Sevabirtinib's dual EGFR/HER2 inhibition leads to significant GI and skin toxicities, making tolerability, not just efficacy, the key factor for clinical preference.

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.

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.

The recent first-line FDA approval of the oral TKI zungertinib fundamentally alters the treatment paradigm for HER2-mutant non-small cell lung cancer. This shifts the standard of care away from initial platinum-based chemotherapy, forcing oncologists to reconsider the sequencing of TKIs, antibody-drug conjugates, and chemotherapy.

While most HER2 mutations in NSCLC occur in the tyrosine kinase domain (TKD), about 20% arise elsewhere. Current HER2 TKIs show high activity against TKD mutations but have significantly lower response rates (~30%) for non-TKD mutations, highlighting an area of unmet need for this patient subset.