Association of MDM2 Overexpression in Ameloblastomas with MDM2 Amplification and BRAFV600E Expression

Abstract

Ameloblastoma is a rare tumor but represents the most common odontogenic neoplasm. It is localized in the jaws and, although it is a benign, slow-growing tumor, it has an aggressive local behavior and high recurrence rate. Therefore, alternative treatment options or complementary to surgery have been evaluated, with the most promising one among them being a targeted therapy with the v-Raf murine sarcoma viral oncogene homologue B (BRAF), as in ameloblastoma the activating mutation V600E in BRAF is common. Studies in other tumors have shown that the synchronous inhibition of BRAF and human murine double minute 2 homologue (MDM2 or HDM2) protein is more effective than BRAF monotherapy, particularly in the presence of wild type p53 (WTp53). To investigate the MDM2 protein expression and gene amplification in ameloblastoma, in association with BRAF^V600E and p53 expression. Forty-four cases of ameloblastoma fixed in 10% buffered formalin and embedded in paraffin were examined for MDM2 overexpression and BRAF^V600E and p53 expression by immunohistochemistry, and for MDM2 ploidy with fluorescence in situ hybridization. Sixteen of forty-four (36.36%) cases of ameloblastoma showed MDM2 overexpression. Seven of sixteen MDM2-positive ameloblastomas (43.75%) were BRAF^V600E positive and fifteen of sixteen MDM2-positive ameloblastomas (93.75%) were p53 negative. All MDM2 overexpressing tumors did not show copy number alterations for MDM2. Overexpression of MDM2 in ameloblastomas is not associated with MDM2 amplification, but most probably with MAPK activation and WTp53 expression. Further verification of those findings could form the basis for the use of MDM2 expression as a marker of MAPK activation in ameloblastomas and the trial of dual BRAF/MDM2 inhibition in the management of MDM2-overexpressing/BRAFV600E-positive/WTp53 ameloblastomas.

Keywords: BRAF; MDM2 protein; ameloblastoma; fluorescence; in situ hybridization; odontogenic tumors; p53.

Figure 1

MDM2 strong (3+) nuclear immunostaining in (A,B) atypical lipomatous tumor and (C) follicular ameloblastoma. Scalebars: red = 50 μm, black = 100 μm.

Figure 2

BRAF^V600E cytoplasmic immunostaining in (A,B) cutaneous melanoma and (C) follicular ameloblastoma. Scalebars: red = 50 μm, black = 100 μm.

Figure 3

Scattered p53 nuclear immunostaining in gingival epithelium (A,B) and (C) in follicular ameloblastoma. Scalebars: red = 50 μm, black = 100 μm.

Figure 4

Fluorescence in situ hybridization (FISH) for MDM2 in a follicular ameloblastoma (ZytoLight-FISH tissue implementation kit). The orange signals represent the probe and the green the control probe. The presence of two orange and two green hybridized signals is representative of euploidy.