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.

Effective treatment of HER2-driven NSCLC requires more than just identifying mutations. HER2 is a multiplexed biomarker where both genetic mutations (TKD and non-TKD) and protein overexpression (via IHC) are independently actionable. Comprehensive testing is crucial to ensure patients are eligible for the full range of available targeted therapies, including TKIs and ADCs.

When a colorectal tumor loses HER2 protein expression (IHC 0) but retains HER2 gene amplification via NGS, the decision to continue HER2-targeted therapy is guided by the amplification copy number. A low copy number argues against continuing the targeted regimen.

Unlike in breast cancer, where HER2 IHC 2+ requires FISH confirmation, in gynecologic cancers an IHC 2+ result is often considered directly actionable for prescribing HER2-targeted ADCs like T-DXD. This reflects a different, less stringent clinical standard for biomarker-guided therapy in this setting.

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.

A negative liquid biopsy (ctDNA) result for HER2 amplification does not prove a patient is HER2-negative. The test's sensitivity is limited by tumor fraction in the blood. While a positive ctDNA result is highly specific and trustworthy, a negative result is simply 'not detected' and requires a tissue biopsy to definitively determine HER2 status for treatment decisions.

While Next-Gen Sequencing (NGS) provides genetic data, IHC directly measures the protein, is faster, cheaper, and requires less tissue. This makes it more scalable for routine clinical use, especially with small biopsy samples. High-level IHC loss correlates well with genetic loss seen on NGS.

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.

When the FDA approves a new biomarker-linked therapy, an in-house pathology lab actively queries its historical database of all prior NGS tests to identify past cases with the relevant genetic alteration. They then proactively contact the oncologists for these patients, uncovering new treatment options that were previously unavailable.