Interphase fluorescence in situ hybridization detection of chromosome 17 and 17q region gains in neuroblastoma: are they secondary events?

Gains of chromosome 17 and 17q region are the most frequent chromosomal abnormalities in neuroblastoma and have been associated with established prognostic indicators. Interphase fluorescence in situ hybridization (FISH) was used to define the status of chromosome 17 in near-triploid (3n) and near-diploid/tetraploid (2n/4n) primary tumors. Gains of chromosome 17 and 17q were detected in 22 and 26 tumors, respectively, in which the ploidy status was determined mainly by the copy number of chromosome 1. Four different types of gains were detected: gain of whole chromosome 17 (+17) and three partial gains (17q11.2 approximately qter, 17q21.1 approximately qter, and 17q21.3 approximately qter). The 17q11.2 approximately qter gains were found in both the 2n/4n and the 3n tumors. Gains of 17q21.1 approximately qter and 17q21.3 approximately qter were found only in the 2n/4n group, and the latter was involved always as a der(22)t(17;22)(q21;q13). A high association was found between chromosome 17 gains and 3n ploidy: +17 was detected in 93% of the 3n group and was not observed in the 2n/4n group. The +17 clone or clones were always present in combination with a clone with normal copies of chromosome 17 and, in the majority, with a +17q11.2 approximately qter clone. We conclude that interphase FISH is a sensitive method for detecting whole and partial chromosome 17 gains in neuroblastoma and can demonstrate the simultaneous presence of several clones with different status of chromosome 17 in 3n neuroblastomas. We suggest that chromosome 17 and 17q gains are not a primary event in the development of neuroblastoma.