*6.1.2. Methods for the detection of 1p/19q chromosomal status*

Different methods for the detection of the 1p/19q chromosomal status are employed in the routine diagnostics. Fluorescent*in situ* hybridization (FISH) is a single-locus technique, limited to the 1p36 locus and thus not regarded as a suitable tool due to the high risk of false-posi‐ tive results [34, 37, 42, 43]. On the other hand, LOH analysis is generally carried out with a low number of microsatellite markers covering only a small chromosomal region.

In contrast, multi-locus techniques, as comparative genomic hybridization (CGH) or multi‐ plex ligation-dependent probe amplification (MLPA) detect gene copy number changes on the whole chromosome and distinguish whole-arm from partial 1p deletion [44]. Additionally, they can reveal putative gain of functions on both 1p and 19q chromosomes [45, 46].

In particular, MLPA has been validated as a high-resolution gene dosage assay for the screening of large deletions and duplication/amplification events in human cancers. In gliomas, three independent studies validated MLPA to assess the 1p/19q status by compar‐ ing MLPA data with CGH data obtained on the same tumor series, mainly composed of oligodendroglial tumors [47–49]. In the authors' experience, MLPA is a reliable and power‐ ful tool to assess the 1p/19q status on formalin fixed and paraffin embedded tumor samples.
