In a tissue sample, in situ hybridization (ISH) techniques identify specific nucleic acid target sequences (DNA or RNA). ISH can also identify genetic anomalies that provide diagnostic and prognostic information. In situ methods offer a high content of information. There are two main types:
- Fluorescent (FISH)
- Chromogenic (CISH)
CISH and silver-enhanced in situ hybridization (SISH) studies for HER2 determine the presence or absence of gene amplification. In most tumors, CISH provides the same result as FISH testing. In some unusual cases, different results are obtained by the alternate counting methods, usually due to a variation in the number of chromosome enumerating probe (CEP) 17 signals.
The fluorescent application, FISH, can detect and localize the presence or absence of specific DNA sequences as in CISH methods but uses a fluorescent chromogen rather than a silver precipitate. FISH is a more established method that is considered the "gold standard." FISH can be used to form a diagnosis, detect diseased cells, evaluate prognosis, or evaluate remission of a disease (cancer). However, both CISH and FISH give quantitative information about the HER2 target.
