Fluorescence in situ hybridization determination of aneusomy: criteria and technical considerations

To investigate a series of tissues to determine if proliferation rate can affect chromosome counts by fluorescence in situ hybridization (FISH).

We studied 9 non-neoplastic tissues and a trisomy 7 and tetrasomy 13 cell line by FISH. For each sample, 100 cells were analyzed for chromosome 7 and 13 number and MIB-1 expression. Centrometric enumeration probe (CEP) 7 counts were correlated with proliferation index.

Average CEP 7 number showed a relationship to proliferation index, with higher CEP 7 averages associated with higher proliferation indices. Specimens of brain tissue demonstrated average CEP 7 counts between 1.64 and 1.75. Tissues with high proliferation indices (23-66%) demonstrated CEP 7 counts between 2.14 and 2.31. The average CEP 7 count for the trisomy 7 cell line was 2.61. The average LSI 13 count for the tetrasomy 13 cell line was 3.65.

Chromosome 7 FISH counts demonstrated overlap between diploid tissues with high proliferation and triploid chromosome 7 tissues. This overlap was seen when 95% CI limits were used. The trisomic 7 and tetrasomic 13 cell lines demonstrated average CEP 7 and CEP 13 levels below 3 and 4, respectively. Definitions used for determination of polysomy should take into account tissue proliferation and section thicknesses.