[933] The Lymphoma-Associated EZH2 Codon 641 Mutation Is Not Detected in Localized Prostate Carcinoma.

Russell J Ryan, Shulin Wu, Darrell Borger, John Iafrate, Chin-Lee Wu, Long Le. Massachusetts General Hospital, Boston

Background: EZH2 encodes the enzymatic subunit of the polycomb repressive complex 2 (PRC2) that mediates gene repression through trimethylation of histone H3 at lysine 27. EZH2 overexpression is associated with poor prognosis in several carcinomas, including prostate carcinoma (PCa). In many cases of advanced PCa, EZH2 overexpression results from genomic deletion of microRNA-101. Recurrent, heterozygous point mutations affecting codon 641 of EZH2 were recently described in a subset of diffuse large B cell lymphomas (DLBCL) and follicular lymphomas (FL). The occurrence of EZH2 codon 641 mutations in PCa has not been previously investigated to our knowlege. While the function of codon 641 mutant Ezh2 protein is not known, the pattern of a heterozygous missense mutation at a stereotyped residue within the enzyme active site suggests a gain-of-function. We sought to determine whether EZH2 codon 641 mutations occur in organ-localized prostate carcinoma, and to determine any association between mutation status and PSA failure in a series of PCa patients with clinical follow-up
Design: Paraffin blocks of tissue from radical prostatectomy performed for prostate cancer were identified from our archives, and foci of PCa were targeted for extraction by punch biopsy, with the highest grade foci targeted whenever possible. Total nucleic acid was extracted, and a 149 bp fragment of genomic DNA containing EZH2 codon 641 was PCR amplified. We then performed SNaPshot single-nucleotide extension genotyping (Applied Biosystems) with 4 extension primers designed to interrogate the 1st 2 nucleotides of EZH2 codon 641 on both the coding and noncoding strand. Extension products were analyzed by capillary electrophoresis. To date, this assay has been validated on 142 paraffin-embedded lymphoma samples, with 21 EZH2 codon 641 mutant lymphoma samples detected, representing four different amino acid substitutions.
Results: Overall, 92 cases of PCa were successfully analyzed. Gleason scores (GS) for analyzed cases were as follows: GS ≤ 3+3 n=50, GS 3+4 n=17, GS 4+3 n=9, GS ≥ 4+4 n=16. Primary tumor stage was pT2 (n=55) or pT3 (n=37). 10-year clinical follow-up showed PSA failure in 29/92 cases. EZH2 codon 641 mutations were not detected in any case (0/92). Clear wild-type genotype signals were seen from all samples.
Conclusions: EZH2 codon 641 mutations are rare or absent in organ-localized prostate carcinoma. Oncogenic disregulation of EZH2 seems to occur by different genetic mechanisms in prostate carcinoma and B cell lymphomas.
Category: Genitourinary (including renal tumors)

Monday, February 28, 2011 1:00 PM

Poster Session II # 146, Monday Afternoon


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