What is the role of FISH in the surveillance for recurrent bladder cancer?

Updated: Sep 10, 2019
  • Author: David A Levy, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Detection of specific DNA alterations known to be associated with bladder cancer is possible using multitarget FISH. DNA probes (stains) hybridize with abnormal chromosomal sites and may be visualized using fluorescence microscopy. According to several published articles, FISH has significantly greater sensitivity than conventional cytology while maintaining the known high specificity of cytology.

The DNA probes chosen for available FISH testing are based on the highest-yielding combination of chromosomal abnormalities. Three of these are centromeric enumeration probes, which allow rapid determination of aneuploidy of chromosomes 3, 7, and 17, the most commonly related to bladder cancer. The fourth probe is used to label the 9p21 locus, known to be the site of a significant tumor suppressor gene. Loss of this tumor suppressor gene is also related to cancer recurrence and progression. A positive result is defined as a gain of 2 or more chromosomes (3,7, or 17) in 4 cells, isolated loss of 9p21 in 12 cells, or isolated gains of only 1 chromosome in 10% or more cells. Most FISH-positive patients develop recurrent urothelial carcinoma within 1 year.

Among patients with bladder cancer in whom cytology results were negative, atypical, and suggestive, FISH detected 60%, 89%, and 100%, respectively, allowing identification of cancer in most patients in whom cytology failed to detect cancer recurrence.

Data from the Mayo Clinic indicate that a conversion of FISH results from positive to negative during bacillus Calmette-Guérin (BCG) therapy indicates a response, whereas a failure to convert indicates a high likelihood of cancer persistence following BCG therapy. [9]

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