Table 6. Terms and definitions for segmental chromosome aberrations of I-FISH results.

Segmental chromosome aberrations analysed by I-FISH
Terms	Description	Comments
Normal status	Balanced ratio between the signal numbers of the chromosomal region of interest and the reference signals on the opposite arm of the chromosome	In the case of a 2/2 ratio, an isodisomy with a complete LOH of all loci located on the investigated chromosome cannot be excluded. However, uniparental isodisomies are extremely rare in NB tumours.
I-FISH imbalance (inconclusive with regard to LOH)	Unbalanced ratio between the signal numbers of the chromosomal region of interest and the reference signals with more than one signals of the chromosomal region of interest	Does not necessarily correspond to an LOH, and is therefore called inconclusive. PCR should be performed to clarify this result. In NB tumours, imbalances frequently, but not always, reflect LOH. Fluorescence in situ hybridisation imbalances can also occur focally. Interphase fluorescence in situ hybridisation imbalances should only be diagnosed if hybridisation failure can be excluded. At least 200 cells should be evaluated.
Deletion	Unbalanced ratio between the signal numbers of the chromosomal region of interest and the reference signals with only one signal of the chromosomal region of interest	This hybridisation pattern corresponds to an LOH. Deletions can also occur focally. Interphase fluorescence in situ hybridisation deletion should only be diagnosed if hybridisation failure can be excluded. At least 200 cells should be evaluated.
Gain	Up to 4-fold excess of signal numbers of the chromosomal region of interest compared with the reference signals
No result	Should be specified: unclear or not interpretable; inadequate tumour cell content; no tumour; Not carried out

I-FISH=interphase fluorescence in situ hybridisation.