For extrahepatic cholangiocarcinoma, obtaining a sufficient tissue sample for diagnosis and molecular profiling can be extremely difficult. Circulating tumor DNA (ctDNA) testing, or liquid biopsy, serves as a crucial alternative in these cases, providing a non-invasive method to secure a diagnosis and identify actionable mutations when a traditional tissue biopsy is not feasible.

Historically considered "heresy," re-biopsy in pancreatic cancer is now an everyday practice. Initial samples often yield insufficient tissue for comprehensive genomic analysis, making subsequent biopsies of metastatic sites necessary to guide precision treatment.

High concordance exists between liquid and tissue biopsies (~89%) for PIK3CA mutations. However, since each method can uniquely identify mutations in some cases, using both liquid and tissue offers the most comprehensive detection strategy to determine patient eligibility for PI3K inhibitors and avoid false negatives.

Dr. Wander favors liquid biopsies for tracking disease progression because they are safer and easier for patients. While acknowledging that tissue biopsies can sometimes detect mutations missed by liquid ones (10-30% discordance), he believes rapidly advancing technology will soon minimize these discrepancies, making them the standard for monitoring.

To maximize the chances of successful biomarker identification from a liquid biopsy, especially when tissue is scant, the blood sample must be drawn before initiating any chemotherapy. This pre-treatment timing is critical for improving the diagnostic yield of blood-based next-generation sequencing (NGS) testing.

Unlike invasive tissue biopsies that sample a single site, liquid blood biopsies provide a comprehensive, real-time snapshot of mutations across all metastatic sites. This is crucial for identifying acquired mutations and guiding timely treatment decisions.

In managing progressive NSCLC, re-biopsy of the tumor is ideal but often fails to yield enough tissue. A presented case study shows liquid biopsy (ctDNA) as a critical alternative, successfully identifying resistance mechanisms to inform subsequent treatment choices when tissue is unavailable.

When an oncologist anticipates an initial sample (e.g., cytology) will likely have insufficient tissue for NGS testing, they proactively initiate a biopsy of a second site with interventional radiology. This parallel-path approach avoids waiting for the first test to fail, significantly reducing time to diagnosis and treatment.

Despite the risk of missing mutations, oncologists predominantly use convenient, less-invasive liquid biopsies to test for biomarkers at disease progression. A more invasive tissue biopsy is generally reserved for situations where the cancer behaves unexpectedly, such as a sudden shift from bone-only to visceral disease, which might suggest a missed biological driver.