Relying solely on Next-Generation Sequencing (NGS) is insufficient for HER2 testing in biliary tract cancers. Data shows NGS misses up to 15% of patients with HER2 overexpression detected by immunohistochemistry (IHC). Performing both tests is essential to avoid denying patients effective targeted therapies.

Comprehensive molecular testing (PD-L1, EGFR, ALK) is no longer reserved for advanced disease. It is now critical for all patients with stage 1B or higher resectable NSCLC *before* starting any treatment to guide neoadjuvant and adjuvant therapy decisions.

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.

While liquid biopsies are a valuable, less invasive tool, a negative result is inconclusive for ruling out actionable mutations in NSCLC. It may simply mean the tumor isn't shedding enough DNA. Therefore, a negative liquid biopsy should never be the final word; it must be followed by a tissue biopsy to ensure patients don't miss out on targeted therapies.

NGS testing is revealing that acquired HER2 kinase domain mutations, not amplifications, are an emerging resistance mechanism in ER+ lobular breast cancer. This creates a targetable population for HER2 TKIs like neratinib or tucatinib, offering a new line of targeted therapy.

Oncologists distinguish between HER2 amplification (the target for ADCs like TDXD) and activating mutations. A patient whose tumor loses amplification but retains a mutation is considered "HER2 mutated," not "HER2 positive," and is generally not a candidate for ADC therapy.

Clinicians ordering "NGS for lung" often misunderstand that Next-Generation Sequencing alone does not cover all actionable biomarkers, such as PD-L1 or HER2. This requires pathologists to interpret the clinician's intent and order a more comprehensive and appropriate test panel.

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.

Patients with HER2-positive GI cancers can lose expression after treatment. While re-biopsy is ideal, it's often impractical or risky. In these cases, clinicians find ctDNA analysis of HER2 copy numbers to be a reliable alternative for guiding subsequent treatment decisions.