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Fluorescence In-Situ Hybridization (FISH)

Fluorescence in situ Hybridization (FISH) analysis offers one of the most sensitive, specific reliable and fast strategy for identifying acquired chromosomal changes for enhanced diagnosis and better management of patient. FISH technique has proved to be very useful in many hematological disorders (CML, ALL, AML, Multiple Myeloma), solid tumors (breast cancer, lung cancer, neuroblastoma, burkits lymphoma) and detecting suspected cases of genetic disorders causing birth defects (downs syndrome) both prenatally and postnatal after birth.

Advantages of FISH technique

  • FISH can be performed on uncultured nuclei (non-dividing cell) at interphase stage of cell cycle and normally results are available with 24 hours using overnight procedures- RAPID Detection.
  • FISH can be performed on variety of samples types including fixed cells from peripheral blood or bone marrow, blood and bone marrow smears, touch preparations and fresh frozen paraffin embedded (FFPE) sections.
  • FISH can detect chromosome abnormalities that are submicroscopic microdeletion even in the interphase cells detecting cryptic or masked balanced or unbalanced translocations.

Figure: The schematic diagram of FISH process showing labeling of BAC/PAC clones with fluorescent dyes for the targeted gene followed by procedure to detection on the target sample

Methodology

Figure: (A) Metaphase FISH for detection of BCR-ABL gene fusion (B) Interphase cell showing FISH signal with 1 F, 2 R, 1 G signal for BCR-ABL gene in chronic myeloid leukemia (CML) patient.

Why Her2/Neu FISH Testing is Important?

  • HER2 gene (also referred as ERBB2) amplification and overexpression are observed in approximately 20-25% of invasive breast cancers
  • ERBB2 status is most often used to determine patient eligibility for trastuzumab immunotherapy one of the most effective treatment for breast cancer. Her2 testing is of great importance to both patient & clinician since trastuzumab is effective only for patients whose Her2 FISH test positive.
Avg. HER2/CEP 17 Ratio=9.7 (Amplified)
POSITIVE
Avg. HER2/CEPRatio=1.3 (Non-Amplified)
NEGATIVE