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.

There's a growing recognition that the molecular profile of a primary tumor can differ significantly from its metastases. To guide treatment more accurately, the preferred practice is to biopsy an accessible metastatic lesion when possible, as this better reflects the biology of the active disease being treated.

While Next-Generation Sequencing (NGS) is routinely performed for young patients with epithelioid sarcoma, experienced clinicians note it seldom uncovers additional actionable mutations. The primary consistent finding is the SMARCB1 loss. This suggests that while NGS is part of comprehensive care, the likelihood of identifying other targetable pathways is currently very low.

ctDNA testing (liquid biopsy) is more effective than tissue biopsy for identifying ESR1 mutations. It samples DNA from all metastatic sites, capturing the disease's genetic heterogeneity and reflecting the most active resistance mechanisms, unlike a single-site needle biopsy which can miss them.

Standard Next-Generation Sequencing (NGS) reports often just state "MET amplification" without a specific copy number. To make informed treatment decisions with MET inhibitors, clinicians must proactively contact the testing company's molecular pathology department to obtain this crucial, unlisted data point.

Dr. Bardia emphasizes that ESR1 is an 'acquired alteration,' meaning the mutation can develop during treatment. This necessitates a shift from one-time diagnostic testing to a dynamic, serial testing model. Repeat testing is critical to identify these actionable mutations as they arise, allowing patients to access newly approved targeted therapies.

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.

In mixed histology bladder cancers treated with standard urothelial therapy, the variant component (e.g., squamous) is hypothesized to be the source of the resistant clone that emerges after treatment. This suggests post-progression biopsies are key to understanding resistance.

Tumor-informed assays like Signatera sequence a patient's tumor to create a personalized test, making it highly sensitive but taking 3-4 weeks. Tumor-uninformed assays are faster (1 week) but less sensitive as they screen for a generic panel of cancer mutations.