Fluorescence in situ hybridization for MDM2 gene amplification as a diagnostic tool in lipomatous neoplasms

Abstract

Well-differentiated liposarcoma/atypical lipomatous tumor and dedifferentiated liposarcoma can be difficult to distinguish from benign lipomatous neoplasms and other high-grade sarcomas, respectively. Cytogenetics in these tumors has identified ring and giant chromosomes composed of 12q13-15 amplicons including the MDM2 gene. Identifying MDM2 amplification by fluorescence in situ hybridization may prove an adjunctive tool in the diagnosis of lipomatous neoplasms. Dual color fluorescence in situ hybridization employing a laboratorydeveloped BAC label probe cocktail specific for MDM2 (12q15) and a probe for the centromeric region of chromosome 12 (Abbott Molecular, DesPlaines, IL) was performed on formalin-fixed and paraffin-embedded tissue including whole sections from atypical lipomatous tumors (n ¼ 13), dedifferentiated liposarcomas (n ¼ 14), benign lipomatous tumors (n ¼ 30), and pleomorphic sarcoma, not otherwise specified (n ¼ 10), and a tissue microarray containing a variety of high-grade sarcomas (n ¼ 63). An MDM2/chromosome 12 ratio Z2.0 was considered amplified, o2.0 nonamplified, and cases displaying 42 signals of both probes and an MDM2 ratio o2.0 polysomic for chromosome 12. Of the well-differentiated and dedifferentiated liposarcomas, 100% showed amplification of MDM2. Chromosome 12 polysomy was noted in 89% of spindle cell/pleomorphic lipomas, while all angiolipomas and lipomas were nonamplified and eusomic. MDM2 amplification was observed in 40% of pleomorphic sarcomas and a small subset of high-grade sarcomas (3/63). MDM2/chromosome 12 fluorescence in situ hybridization is a sensitive and specific tool (both 100%) in evaluating low-grade lipomatous neoplasms. The specificity decreases in high-grade sarcomas, as MDM2 amplification was observed in a small portion of pleomorphic sarcomas and high-grade sarcomas other than dedifferentiated liposarcomas. Importantly, none of the benign lipomatous lesions were MDM2 amplified and even cells in areas of well-differentiated liposarcomas with minimal cytologic atypia were amplified, making the probe a valuable tool in the diagnosis of even limited biopsy samples of well-differentiated lipomatous neoplasms.

Sensitivity of MDM2 amplification and unexpected multiple faint alphoid 12 (alpha 12 satellite sequences) signals in atypical lipomatous tumor

“…[5][6][7][8][9][10]20 As a consequence, the identification of this molecular abnormality is advocated as a useful ancillary diagnostic marker, and can be considered 100% specific in the appropriate clinical and histological context. 9 Our data support the findings of others and shows that there is a good correlation between microscopic diagnosis and MDM2 amplification status.…”

“…[5][6][7][8][9][10]20 As a consequence, the identification of this molecular abnormality is advocated as a useful ancillary diagnostic marker, and can be considered 100% specific in the appropriate clinical and histological context. 9 Our data support the findings of others and shows that there is a good correlation between microscopic diagnosis and MDM2 amplification status. [5][6][7][8][9][10] As in the study by Zhang et al 10 we found that we had a tendency to 'overcall' lipomas, whereas the risk of 'under-calling' an atypical lipomatous tumor (MDM2 amplification-positive) was much less.…”

“…A ratio of 42.0 was considered to represent amplification (amplification-positive), a ratio of 2 was considered to be non-amplified (amplification-negative). 9 Regardless of the MDM2:centromere 12 or CDK4:centromere 12 ratio, an average of 3 or more signals for centromere 12 was considered to represent copy number gain (referred by others previously as aneusomy or polysomy). 9 All FISH was reviewed by at least two individuals experienced in interpreting FISH.…”

“…By applying the strict definition for identifying tumors with MDM2 amplification (see Materials and methods), 9 we found that 14% (13 of 92) of tumors classified on histological grounds as atypical lipomatous tumor did not reveal MDM2 amplification. MDM2 amplification was then sought on an additional four slides in each of these cases, and a single slide from one tumor (12 cm in the thigh) revealed extensive MDM2 amplification.…”

“…2 A number of studies have shown that there is a strong correlation between the presence of supernumerary ring or giant marker chromosomes, derived from chromosome 12q13-15 where MDM2, CDK4, SAS, HMGIC and other genes are located, and the morphological features of atypical lipomatous tumors and dedifferentiated liposarcomas. These genetic abnormalities, originally reported using cytogenetics, 3,4 and subsequently by reverse transcription polymerase chain reaction, [5][6][7] fluorescence in situ hybridization (FISH), [8][9][10] and later with antibodies to MDM2 and CDK4, 5,8 demonstrated that MDM2 amplification occurs consistently in atypical lipomatous tumor in which CDK4 is also frequently amplified. In contrast, other genes in the chromosomal region 12q13-15 are less commonly associated with copy number gain 11,12 and in a small number of cases CDK4 amplification has been reported in the absence of MDM2 copy number gain.…”