Transcript MDM2 +/P53 -/MIB-1 High

Frequency of MDM2 Amplification in Malignant Peripheral Nerve Sheath Tumors:
Non-Correlation with Tumor Grade, Cellularity and MIB1 Proliferation Index
Michelle L.
1ARUP
2Department
Introduction
1
Wallander ,
Sheryl
1
Tripp
and Lester J.
2
Layfield
Institute for Clinical and Experimental Pathology, ARUP Laboratories, Salt Lake City, UT
of Pathology, University of Utah Health Sciences Center and ARUP Laboratories, Salt Lake City, UT
Results
Results
 Three of fifteen (20%) MPNSTs demonstrated MDM2 gene
amplification.
The MDM2 oncogene has been shown to be upregulated in a
number of human neoplasms as a result of gene amplification,
increased transcription or increased translation. Upregulation of
MDM2 can result in p53 inactivation and represents a separate
mechanism in addition to p53 mutation for inhibition of p53 function.
Such p53 inactivation can lead to uncontrolled cell proliferation and
tumor growth.
 Four of fifteen (27%) MPNSTs had high positivity for p53 protein
expression.
 All three MDM2 amplified MPNSTs showed high expression of
p53, which was statistically significant (p = 0.004).
Although MDM2 gene amplification has been shown to occur in up
to 7% of all human tumors, soft tissue tumors account for the
majority (20%). MDM2 amplification and overexpression have been
most diagnostically useful in separating lipomas (MDM2 nonamplified) from well-differentiated liposarcomas/atypical lipomatous
tumors (MDM2 amplified). Prior reports on the percentage of
malignant peripheral nerve sheath tumors showing MDM2
overexpression or amplification have documented variable findings.
The p53 and MDM2 proteins function in the same cell proliferation
pathway and have directly antagonistic functions. Thus, some
authors have hypothesized that neoplasms would be either p53
mutant or MDM2 amplified. Most immunohistochemical data for
p53 and MDM2 protein expression support this premise with only
7.9% of tested soft tissue sarcomas expressing both p53 and
MDM2. In a study of 115 soft tissue sarcomas, the p53-/MDM2+
phenotype predominated (20% of cases) with only 1.8% of tumors
being p53+/MDM2-. Because p53 expression correlates with high
histologic grade and proliferation index, p53 mutation was assumed
to be a late event. MDM2 amplification was assumed to be a
relatively early event since it did not correlate with either grade or
proliferation index.
Given the variable reports of MDM2 amplification and p53
dysregulation in MPNSTs, we studied a series of fifteen MPNSTs
and fifteen control schwannomas. The percentage of MPNSTs
demonstrating MDM2 amplification was determined and correlated
with p53 protein expression, MIB-1 proliferation index and tumor
cellularity.
Materials and Methods
 15 FFPE MPNSTs and 15 FFPE schwannomas were selected
from the University of Utah surgical pathology files.
 Ki-67 IHC: mouse monoclonal, clone MIB-1 (Dako)
High positivity: > 15% of cells positive
 p53 IHC: mouse monoclonal, clone DO-7 (Dako)
High positivity: > 20% of cells positive
 MDM2 FISH: MDM2 (12q15) / SE 12 Repeat-Free™ Poseidon™
FISH probe (Kreatech)
 Non-amplified: MDM2/SE12 ≤ 2.0
 Amplified: MDM2/SE12 > 2.0
 Statistics: Fisher’s exact test
 The use of human tissue for this analysis was approved by the
University of Utah Institutional Review Board (#22487).
MDM2 FISH amplified (Case 12)
 The majority of MPNSTs (73%) were negative for both MDM2
amplification and p53 expression.
MDM2 FISH non-amplified (Case 14)
 MIB-1 IHC was positive in 10 of 15 MPNSTs (67%).
 All three MDM2 amplified MPNSTs were associated with a high
proliferation rate (MIB-1) but this did not reach statistical
significance (p = 0.374).
 Tumor cellularity was high in 11 of 15 (73%) of MPNSTs.
p53 low expression
p53 high expression
Low MIB-1
proliferation index
High MIB-1
proliferation index
 All three MDM2 amplified MPNSTs had high cellularity but the
association was not statistically significant (p = 0.335).
Representative images of MDM2 FISH, p53 IHC and MIB-1 IHC (FISH, x1000; IHC, x200).
 None of the fifteen schwannomas were characterized by MDM2
amplification, high p53 protein expression or a high MIB-1
proliferation index.
Results
Conclusions
MPNST
Case 1
Case 2
Case 3
Case 4
Case 5
Case 6
Case 7
Case 8
Case 9
Case 10
Case 11
Case 12
Case 13
Case 14
Case 15
MDM2/SE12 Ratio
(amplified status)
2.12 (amplified)
1.10 (non-amplified)
1.08 (non-amplified)
0.96 (non-amplified)
1.50 (non-amplified)
1.22 (non-amplified)
1.20 (non-amplified)
1.33 (non-amplified)
1.12 (non-amplified)
1.02 (non-amplified)
1.03 (non-amplified)
16.5 (amplified)
9.19 (amplified)
1.04 (non-amplified)
0.98 (non-amplified)
Marker Expression
MDM2 +/P53 +/MIB-1 High
MDM2 +/P53 -/MIB-1 High
MDM2 +/P53 +/MIB-1 Low
MDM2 +/P53 -/MIB-1 Low
MDM2 -/P53 +/MIB-1 High
MDM2 -/P53 -/MIB-1 High
MDM2 -/P53 +/MIB-1 Low
MDM2 -/P53 -/MIB-1 Low
MIB-1 Level
(%)
High (45%)
High (28%)
High (70%)
High (40%)
Low (4%)
Low (6%)
High (19%)
High (28%)
Low (12%)
Low (13%)
High (19%)
High (26%)
High (41%)
High (35%)
Low (5%)
P53 Level
(%)
High (55%)
Low (10%)
High (79%)
Low (0%)
Low (7%)
Low (10%)
Low (11%)
Low (4%)
Low (15%)
Low (0%)
Low (0%)
High (36%)
High (23%)
Low (20%)
Low (0%)
# MPNST Cases
3
0
0
0
1
6
0
5
Cellularity
High
High
High
High
Low
Low
High
High
High
Low
High
High
High
High
Low
Percentage of
Total Cases
20%
0%
0%
0%
7%
40%
0%
33%
The low frequency of MDM2 amplification in our series of MPNSTs
(20%) demonstrates that MDM2 FISH has limited diagnostic value
for the separation of benign and malignant peripheral nerve sheath
tumors.
According to prior studies, MDM2 amplification rarely coexists with
p53 protein expression in MPNSTs. Our study demonstrates a
positive correlation (p = 0.004) between MDM2 amplification and
p53 expression as all three MDM2 amplified cases had high p53
positivity. These results indicate that p53 overexpression and
MDM2 gene amplification can coexist, although p53 is likely
inactive. Investigation of p53 mutation status by mutational analysis
is warranted to confirm this hypothesis. As would be expected,
these three MDM2+/p53+ cases also demonstrated high MIB1
proliferation idices and high cellularity, although these associations
did not reach statistical significance.
References
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