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.

Despite emerging trial data, clinicians are not yet ready to change therapy based on ctDNA positivity alone. Key concerns cited include the absence of a proven survival benefit from early intervention, the potential to use future treatment lines prematurely, and overall feasibility. The consensus is that while promising, the technology is not yet ready for routine clinical decision-making.

Given that PD-L1 scores for gastroesophageal cancers can be exceptionally variable between labs, some clinicians prefer a simple CPS cutoff of 1. This 'some expression versus no expression' approach is considered more reproducible and practical for decision-making than relying on specific higher scores that may not be consistent across different testing sites.

The traditional "germinal center" (GC) classification for DLBCL is overly simplistic. Molecular analysis reveals distinct subtypes within GC, such as "dark zone" and "light zone" signatures, which have different prognoses and responses to targeted therapies like polatuzumab.

Beyond clinical validation, the adoption of novel biomarkers like microRNA is hindered by practical lab issues. Disagreements over sample type (serum vs. plasma), establishing universal cutoffs, and achieving high concordance between different testing centers are critical, non-clinical hurdles that must be overcome for widespread clinical use.

For certain therapies like Enhertu, eligibility is based on immunohistochemistry (IHC), not NGS. Labs must run HER2 IHC in parallel because NGS, as a population-based test, can miss intratumoral heterogeneity (small clusters of positive cells) that IHC can detect, thus identifying more eligible patients for targeted therapy.

Clinicians must recognize that liquid and solid biopsies show significant discordance. ESR1 mutations are more frequently detected in liquid assays, while PIK3CA mutations are more often found in solid tissue. This variability by gene directly impacts the optimal testing strategy for patients.

While clinicians often ponder how to prioritize treatments for patients with multiple actionable biomarkers, this scenario is exceedingly rare in practice. The guiding principle, if it does occur, is to choose the therapy with the strongest supporting clinical trial data, though this remains an infrequent dilemma.

Inconsistent methods for assessing biomarkers like PD-L1 (CPS vs. TAP scoring), p53 (IHC vs. sequencing), and HRR (different panels) across major clinical trials make it difficult to compare results and identify a reliable predictive marker for endometrial cancer.