Reclassification of oligoastrocytomas by loss of heterozygosity studies Marica Eoli 1 , Lorena Bissola 2 , Maria Grazia Bruzzone 2 , Bianca Pollo 1 , Carmelo Maccagnano 2 , Tiziana De Simone 2 , Lorella Valletta 2 , Antonio Silvani 1 , D Bianchessi 2 , Giovanni Broggi 3 , Amerigo Boiardi 1 and Gaetano Finocchiaro 2 * 1 Department of Clinical Neurosciences, Istituto Nazionale Neurologico Besta, Milan, Italy 2 Department of Experimental Neurosciences and Diagnostics, Istituto Nazionale Neurologico Besta, Milan, Italy 3 Department of Neurosurgery, Istituto Nazionale Neurologico Besta, Milan, Italy Oligoastrocytomas (OAs) are WHO grade II or III tumors com- posed of a mixture of 2 neoplastic cell types morphologically resembling the cells in oligodendrogliomas and diffuse astrocyto- mas. Investigations on the genetic profile of OAs may yield impor- tant information for their classification and help for their clinical management. We have studied, in 94 OAs (46 WHO grade II and 48 WHO grade III), the patterns of loss of heterozygosity (LOH) of 4 genomic regions: 1p, 19q, 17p and 10q. Results were as fol- lows: LOH 1p was present in 46% of the tumors; LOH 19q in 45%; LOH 17p in 22%; LOH 10q in 16%. LOH 1p and 19q were associated in 32%, other LOH associations were rare (<3%). Patients had a median follow-up of 30 months. Patients without LOH on 1p had shorter progression free survival than patients with LOH on 1p: 30 vs. 132 months, p < 0.0001. MRI indicated that tumors without LOH on 1p were often temporal (p < 0.02), and showed signal inhomogeneity on T1 and T2 images (p < 0.02) and contrast enhancement (p < 0.04). Thus, LOH on 1p identifies two subgroups of OAs. OAs without LOH on 1p behave like WHO grade II or III diffuse astrocytomas: they have shorter survival, MRI characteristics implying malignancy and genetic alterations associated with tumor progression. OAs with LOH on 1p, on the other hand, behave like WHO grade II or III oligodendrogliomas with 1p loss: they are associated with longer survival and do not have MRI or genetic alterations associated with malignancy. These findings suggest that the definition of OAs or mixed gliomas could be reshaped in agreement with the genetic information. ' 2006 Wiley-Liss, Inc. Key words: oligoastrocytoma; LOH 1p; LOH 19q; LOH 17p; LOH 10; MRI Oligoastrocytomas (OA) or mixed gliomas are tumors showing a conspicuous mixture of 2 distinct neoplastic cell types, resem- bling the tumor cells in oligodendrogliomas and diffuse astrocyto- mas. The 2 components may be separated into distinct areas or diffusely admixed. 1 A pathological diagnosis based on the assessment of the indi- vidual components is difficult, since in most instances the true extent of each component is impossible to determine because of incomplete tumor sampling. In addition, the tumor cells may not always be clearly recognized as either oligodendroglial or astro- cytic, i.e. they may have features of both lineages. 2,3 Oligodendro- gliomas and oligoastrocytomas can be classified as WHO grade II or WHO grade III tumors. WHO grade III OA show signs of ana- plasia: nuclear atypia, cellular pleomorphism, high cellularity and high mitotic activity. Signs of histological malignancy may be present in the all the components of the tumor (oligodendroglial, astroglial or both). 1 Glioma genotyping can provide important information comple- menting the histological analysis. Genetic alterations of OA include loss of heterozygosity (LOH) on chromosome 1p and/or 19q, typical of oligodendrogliomas 4 but also loss of heterozygos- ity on chromosome 10q and/or 17p, frequently found in astrocyto- mas and associated with the progression to glioblastoma. 5 LOH of 1p and/or 19q has been associated with chemosensitiv- ity and prolonged survival, 6,7 while LOH of 10q has an unfavora- ble impact on prognosis. 8 We have studied the clinical, genetic, histological and radiolog- ical features of 94 mixed gliomas diagnosed in our Institution from 1992 through 2003, to verify if such combined analysis could yield diagnostic and prognostic criteria helpful to obtain a more informative classification for these tumors. Results point to a criti- cal role for the allelic imbalance on the p arm of chromosome 1 in the reclassification of WHO grade II and III oligoastrocytomas. Patients and methods Tumor and corresponding blood samples were obtained from 94 patients with oligoastrocytoma, treated at the Istituto Nazionale Neurologico Carlo Besta, Milan, between 1992 and 2003. Genetic and preliminary clinical data of 34 of these patients were reported in a previous paper. 8 The pathological diagnosis was performed in agreement with WHO classification of brain tumors 1 by 2 neuropathologists of our Institution. The diagnosis was made when the tumor contained neoplastic cells of astrocytic and oligodendrocytic morphology and 1 of these 2 populations represented at least 25% of the neo- plastic cells. The study included 46 oligoastrocytomas (OAs, WHO grade II) and 48 anaplastic oligoastrocytomas (AnOAs, WHO grade III). These selection criteria were considered: (i) newly diagnosed, untreated sovratentorial oligoastrocytomas, excluding those aris- ing in the pons, medulla or optic chiasm; (ii) total or subtotal resection of the tumor; (iii) treatment by at least one cycle of chemotherapy; (iv) periodical clinical and radiological follow-up in our Institution. Tumors with clearly recognizable gemystocytes were excluded from the analysis. Clinical data are summarized in Table I. The 94 patients (52 males and 42 females) had a mean age of 41 years at the diagnosis (range 20–68). After surgery, clinical and neuroradiological con- trols were performed every 6 months at our Institution. Progres- sion Free Survival (PFS) was considered in addition to Overall Survival (OS) to study the prognosis. All patients were treated by at least one cycle of chemotherapy with procarbazine–cyclohexyl- chlorethylnitrosureas–vincristine (PCV) or bis-chlorethylnitro- surea and cisplatinum. Patients with AnOAs investigated from 1992 through December 2000 were also treated by radiotherapy, consisting of a median dose of 56.5 Gy delivered with a 15 MV photon beam LINAC in 1.8–2.0 daily fractions. The treatment vol- ume encompassed the contrast-enhancing lesion on the preopera- tive MRI with a 2 cm margin: if the tumor had no contrast enhancement, the target was defined on the T2 weighted pre-oper- atory MRI scan plus a 2 cm margin. From January 2001 WHO grade III tumors showing losses on 1p and/or 19q received chemo- therapy only and radiotherapy at recurrence. Overall, radiotherapy soon after surgery was performed in 35 patients. Eighteen patients (12 OAs and 6 AnOAs) out of 39 with a recurring tumor had a sec- ond surgery: 5 of these 18 had histological features of glioblas- toma multiforme. All patients with a recurring tumor received sec- Grant sponsor: Ministero della Salute *Correspondence to: Unit of Experimental Neuro-Oncology, Dept. Ex- perimental Neurosciences, Istituto Nazionale Neurologico Besta, via Celo- ria 11, 20133 Milan, Italy. E-mail: finocchiaro@istituto-besta.it Received 6 June 2005; Accepted 25 October 2005 DOI 10.1002/ijc.21759 Published online 23 January 2006 in Wiley InterScience (www.interscience. wiley.com). Int. J. Cancer: 119, 84–90 (2006) ' 2006 Wiley-Liss, Inc. Publication of the International Union Against Cancer