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Molecular Profiling in Oncology: A Deep Dive into Testing Methods

• 0:00:14 Introduction: Molecular profiling, identifying tumor-specific genetic changes, is crucial for targeted cancer therapies, personalized care plans, and improved patient outcomes.

• 0:00:45 Definition: Molecular profiling involves testing tissue or biofluid samples (serum, plasma, urine) to identify tumor-specific molecular alterations.

• 0:01:00 Common Technologies: Several technologies are used, including:

  • Karyotyping
  • Immunohistochemistry (IHC) / Immunocytochemistry (ICC)
  • Fluorescence in situ hybridization (FISH)
  • PCR-based assays
  • Sanger sequencing
  • Next-generation sequencing (NGS)

• 0:01:28 Karyotyping: This older method stains and pairs chromosomes to detect large-scale abnormalities. It has low resolution (5-10 megabases) and cannot detect small changes, making it largely obsolete in modern pathology.

• 0:02:20 Immunohistochemistry (IHC) / Immunocytochemistry (ICC): These methods use probes to visualize target proteins within cells. Widely used in diagnostics, they have low resolution but are slightly better than karyotyping.

• 0:03:04 Fluorescence In Situ Hybridization (FISH): This method uses fluorescently tagged DNA/RNA sequences to bind to specific genetic alterations (translocations, inversions, deletions, duplications), visualized with a fluorescence microscope. It has low resolution.

• 0:03:38 PCR-Based Assays: These assays amplify specific DNA regions using primers. They offer much higher resolution than previous methods. Variations, such as real time quantitative PCR, and reverse transcription PCR (RT-PCR), can detect RNA and assess gene expression.

  • Can detect known mutations or mutations in "hotspot" regions.
  • Also used to detect insertions/deletions via fragment analysis.

• 0:05:09 Gene Sequencing (Sanger and NGS): Both offer high-resolution sequencing.

  • Sanger Sequencing: The first practical DNA sequencing method, still used today, but sequences only one DNA fragment at a time.
  • Next-Generation Sequencing (NGS): Sequences millions of fragments simultaneously, enabling fast and cost-effective sequencing of multiple genes.

• 0:06:07 NGS Advantages:

  • Can detect the full range of genetic modifications.
  • Allows interrogation of single genes, gene panels, all protein-coding regions (exome), or the entire genome.
  • Can detect unforeseen genetic aberrations, unlike PCR-based assays that target predefined mutations.

• 0:06:44 NGS Challenges: Interpreting the large amount of output data can be difficult.

• 0:06:51 NGS in Clinical Practice: Gaining traction, though routine implementation may not be universal yet. Cost can be managed by running sufficient testing volumes (e.g., 400 samples/year) or using focused gene panels.

• 0:07:28 Biomarker test of choice If cost can be justified, NGS is the biomarker test of choice.