[1510] Assessment of the 1p/19q Deletions at Different Areas in Biphasic Oligoastrocytomas by Using Chromogenic In Situ Hybridization

VC Oliveira, RCV Carrara, DT Covas, EF Latorraca, CG Carlotti, Jr, BO Colli, HR Machado, L Neder. Faculty of Medicine of Ribeiro Preto, Ribeiro Preto, Brazil

Background: Oligoastrocytomas (OAs) are mixed gliomas composed of tumor cells morphologically resembling oligodendroglioma and diffuse astrocytoma. Albeit the status of 1p/19q deletions in oligodendrogliomas is well-known, isolated or combined losses of 1p/19q in OA remains to be elucidated. The goal of this study was to evaluate the 1p/19q deletions by using CISH at different tumor areas in a series of bona fide biphasic OAs of different grades of malignancy.
Design: CISH was performed on formalin-fixed paraffin-embedded cores in different tumor areas of 12 OA, intermingled (diffuse) variant (4 grade II, and 8 grade III) by using a TMA block . The patient's mean age was 40 years (11-54 years) with 2:1 male/female ratio. The presence or absence of chromosome locus 1p36 and 19q13 was analized in different tumor areas [oligo vs astrocytic areas]. The cut-off values was established by counting 500 nuclei in normal brain tissue from patients with intractable epilepsy. It was analyzed a minimum of 200 tumor nuclei for each set of probes without the knowledge of the diagnosis.
Results: Were have found combined/isolated losses of 1p/19q in 50% of the tumor samples.

Table 1. Status of 1p/19q deletions in Oligoastrocytomas according different grades of malignancy.

Grade	1p/19q	1p	19q	No deletions	Total
II	1	1		2	4
III	1	2	1	4	8

The combined 1p/19q losses were detected in 2/12 cases and were present in both astrocytic and oligodendroglial components. The isolated loss of 1p was detected in 3/12 cases (25.0%). Interestingly, the 1p loss was present in both components in one grade III OA. The remainder exhibited isolated 1p loss in astrocytic but not in the oligodendroglial area (grade II) and vice-versa (grade III OA). The isolated loss of 19q was found in both components and it was present in one case.
Conclusions: 1p/19q deletions are not an uncommon event in OAs. Interestingly, in these cases, regardless if they have combined or isolated losses, the chromosomical deletions were found in both oligo and astrocytic components in 4/6 cases, which could reflect the clonal origin for both components. Furthermore, CISH is a low-cost technique, easy to perform and has a beneficial tool in the diagnosis assessment of 1p/19q status in gliomas.
Category: Neuropathology

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 194, Tuesday Morning