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CDKN2A/p16 in ependymomas
S Bortolotto1, L Chiadò-Piat, P Cavalla
1Department of Neuroscience, University of Turin, Italy.
Abstract:
Sixteen cases of ependymoma were studied for CDKN2A/p16 inactivation by immunohistochemistry using a p16 monoclonal antibody, by homozygous deletion (HD) assay and 5'CpG promoter methylation assay (methylation-specific PCR). Three out of 16 cases were p16 immuno-negative: two corresponded to grade II ependymomas and one to grade III. The latter ependymoma, characterized by a high Ki-67/MIB-1 LI, was the only one of the whole series to show CDKN2A HD. No promoter methylation was found in the two immuno-negative cases without CDKN2A HD. Alternative mechanisms, such as point mutations or alterations in p16 post-translational regulation, may be responsible for p16 inactivation. Since in our series just one out of eight anaplastic cases showed negative immunostaining and CDKN2A HD, p16/CDKN2A inactivation may not play an important role in the malignant transformation of ependymomas. Amplification of CCNDI and CDK4, p27/Kipl degradation and TP53 mutations were previously studied by other authors and were demonstrated not to correlate with anaplasia. Up to date, molecular genetic studies have not been useful in recognizing the anaplastic variant in ependymomas.
Insights
CDKN2A/p16 inactivation was studied in 16 ependymoma cases. Inactivation was rare and did not appear to drive malignant transformation in ependymomas.
Area of Science:
- Neuro-oncology
- Molecular Pathology
- Cancer Genetics
Background:
- Ependymomas are primary tumors of the central nervous system.
- Understanding the molecular alterations in ependymomas is crucial for diagnosis and treatment.
- CDKN2A/p16 is a tumor suppressor gene frequently altered in various cancers.
Purpose of the Study:
- To investigate the role of CDKN2A/p16 inactivation in ependymoma pathogenesis.
- To determine the frequency of CDKN2A/p16 inactivation in different grades of ependymoma.
- To explore potential mechanisms of p16 inactivation in ependymomas.
Main Methods:
- Immunohistochemistry using a p16 monoclonal antibody.
- Homozygous deletion (HD) assay for CDKN2A.
- 5'CpG promoter methylation assay (methylation-specific PCR).
Main Results:
- Three out of 16 ependymoma cases showed p16 immuno-negativity (2 grade II, 1 grade III).
- The single grade III ependymoma case with p16 immuno-negativity exhibited CDKN2A HD.
- No promoter methylation was detected in immuno-negative cases lacking CDKN2A HD.
Conclusions:
- CDKN2A/p16 inactivation appears infrequent in ependymomas.
- Mechanisms other than homozygous deletion or promoter methylation may cause p16 inactivation.
- CDKN2A/p16 inactivation may not be a significant factor in the malignant transformation of ependymomas.