Application of brush cytology for FISH-based detection of 1p/19q codeletion in oligodendroglial tumors

Currently, oligodendroglial tumours (OT) are routinely tested for 1p/19q codeletion, a genetic abnormality of prognostic value. This analysis is most commonly performed by fluorescence in situ hybridization (FISH) on formalin-fixed, paraffin embedded (FFPE) tissue sections, which is time-consuming and often difficult to interpret, mainly due to the presence of truncated and overlapping nuclei. To overcome these methodological disadvantages, we investigated the validity of cytospins prepared from brushings of fresh tissue samples for assessing 1p/19q status by FISH. For this purpose, FISH analysis of 1p/19q codeletion was performed on FFPE tissue sections and cytospins prepared from brushing of corresponding fresh tissue in a series of 35 central nervous system tumours (16 OT and 19 non-OT). An aberrant 1p/19q status was found in 11/16 (69 %) OT samples and included codeletion of 1p/19q (7), 1p/19q imbalance (2) isolated 19q deletion (1) and 1p imbalance (1). None of the 19 non-OT samples showed 1p/19q codeletion. Results of FISH were concordant between FFPE sections and cytospins in all cases in which both types of slides gave interpretable results. Interpretation of FISH signals on cytospins was easier and quicker than on FFPE sections. Our study showed that cytospins prepared from brushing of fresh tissue samples allow quick and reliable FISH based analysis of 1p/19q status and can substitute traditional FFPE sections when fresh tissue is available.