內文：

(1)

口腔病理科 On-Line KMU Student Bulletin

原文題目(出處)： Ameloblastic carcinoma ex ameloblastoma: report of a case–possible involvement of CpG island hypermethylation of the p16 gene in malignant transformation

(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;103:72-6) 原文作者姓名： Abiko Y, Nagayasu H, Takeshima M, Yamazaki M, Nishimura M,

Kusano K, Kitajo H, Saitoh M, Kawakami T, Chib I, Kaku T

通訊作者學校： HEALTH SCIENCES UNIVERSITY OF HOKKAIDO, Sapporo City and Ishikari-Tobetsu, Japan

報告者姓名(組別)： R2陳靜怡

報告日期： 96/04/24

內文：

ABSTRACT

1. Ameloblastic carcinoma

分類：根據 WHO的分類，ameloblastic carcinoma為一種罕見的惡性病變

起源：(1) carcinoma ex ameloblastoma –由已存在之良性ameloblastoma 惡性轉變而來。

(2) de novo carcinoma–as a primary malignant lesion, 一開始即為惡性，非由已存在之良性腫瘤轉而來。

2. 病例報告：a case of ameloblastic carcinoma ex ameloblastoma.

3. 目的：了解此病例惡性轉變(malignant transformation)的原因 4. 方法：(1) 組織病理切片進行免疫化學染色—CK19、p53、Ki67

(2) 抽取出此腫瘤中良性與惡性部分之DNA進行比對 5. 結果：(1) p53基因中exons 5-8沒有發現突變(mutation)

(2)在惡性區域所取出之DNA，p16基因的CpG islands有hypermethylation的現象 6. 結論：p16基因hypermethylation的現象可能與ameloblatoma的malignant transformation

有關。

INTRODUCTION

1. WHO分類之odontogenic carcinomas包含 (1) metastasizing ameloblastoma (2) ameloblastic carcinoma

(3) primary intraosseous carcinoma (4) ghost cell odontogenic carcinoma (5) clear cell odontogenic carcinoma

2. Ameloblastic carcinoma -- 一種罕見的惡性病變，具有特別的組織病理特徵，臨床行為 aggressive。其起源包含下列兩種方式

(1) carcinoma ex ameloblastoma – 由已存在之良性ameloblastoma 惡性轉變而來。可在腫瘤中發現benign ameloblastoma的組織病理特徵。

(2) de novo carcinoma – as a primary malignant lesion, 一開始即為惡性，非由已存在之良性腫瘤轉而來。

3. 與malignant transformation相關的基因突變與分子變化

(1) p53–一種腫瘤抑制基因，在malignant transformation，最常發現p53的突變。

(2) Epigenetic alternation–hypermethylation 為其中一種。腫瘤抑制基因的 CpG islands發生hypermethylation會抑制腫瘤抑制基因的轉錄(transcription)作用。

(a) Hypermethylation of p15與p16 gene (tumor suppressor gene)常在數種惡性腫瘤(包含oral SCC)中被偵測到。

(b) Hypermethylation of E-cadherin promotor 最近也在oral SCC發現。

CASE REPORT

1. Basic data:

(1) Age：72 y/0 (2) Gender：Male

2. Chief complaint：a swelling of the mandible extending form the right molar region to the incisors

- 1 -

(2)

3. Present illness：

This 72 y/o male had noticed the painless swelling in 2002.10. He presented to a dental clinic in 2003.03 (發現該lesion半年後) complaining that his denture no longer fit properly. The dentist found a radiolucent lesion in the mandible, so he was referred to the University hospital

4. PMH：DM, under medication control for 10 years PDH：Denture wearing，type and duration unknown 5. Extra-oral and intra-oral examination

(1) Facial distortion，right lower face swelling

(2) A hard bony swelling in the mandible extending from the right molar region to the incisors.

6. Radiographic imaging and CT–multilocular destruction of bone，cortical thinning，bony expansion，perforation of the right buccal and lingual mandible.

7. Treatment course：

(1) Biopsy

(a) Microscopic findings：epithelial tumor cells resembling odontogenic epithelium in a network-like arrangement.

(b) Provisional diagnosis: follicular ameloblastoma (2) Surgical removal

(a) Tumor size：48 × 65 × 21 mm in size

(b) Microscopic findings：plexiform and solid growth pattern (i) Benign part

The area of plexiform growth was anastomosing strands and cords of cell with a minimal stellate reticulum like component. The border cells were columnar with hyperchromatic nuclei that were polarized away from the basement membrane

(ii) Malignant part

The area of solid growth exhibited the malignant features of the ameloblastoma and was composed of polygonal cells forming anastomosing trabecular nests. The tumor cells were pleomorphic with hyerchromatic nuclei. Moderate atypia and mitoses were observed. In one section of malignant area, rounded cells containing large nuclei and scant cytoplasm formed solid nests

(c) Final diagnosis: ameloblastic carcinoma ex ameloblastoma

MATERIALS AND METHODS

1. Immunohistochemicl stain–CK19(for odontogenic epithelium)、p53、Ki67 2. DNA extraction and PCR( polymerase chain reaction)

(1) extraction of DNA of benign and malignant area from paraffin sections (2) exons 5-8 of p53 isolated，then amplified with PCR kit

(3) Primers sets (Table 1) using to identify mutations

(4) p15、p16 and E-cadherin isolated, then using CpG WISDOM amplification kit (5) Primer sets (table 1) using to distinguish unmethylation (U) and methylation (M)

RESULTS

1. Immunohistochemicl stain

(1) CK19 – most tumor cells were positive in benign and malignant area (2) Ki 67 – malignant area：80% positive each view

benign area：only a few positive nuclei (3) p53 – negative in benign and malignant area

2. Mutation and alternation

(1) exons 5-8 of p53 gene – no mutation (2) CpG island mythylation

(a) p15 – no CpG island mythylation

(b) p16 -- CpG island mythylation found in malignant area

- 2 -

(3)

(c) E-cadherin -- no CpG island mythylation

DISCUSSION

1. DNA methylation

DNA methylation會對環境 (environmental)、生理 (physiological) 與生物 (biological) 訊號 (signals) 產生反應導致改變。在許多惡性腫瘤中，特定基因的 methylation，例如腫瘤抑制基因，會影響DNA的修復。Hypermethylation 與惡性轉變相關

2. WHO classification 2004年將ameloblastic carcinoma 與 metastasizing ameloblastoma 分開獨立為兩種疾病。

(1) Ameloblastic carcinoma 定義：a malignant epithelial proliferation that is associated with an ameloblastoma (ca. ex ameloblastoma) or histologically resembles an ameloblastoma ( de novo carcinoma)

(2) Malignant ameloblastoma定義：a tumor exhibiting the histological features of classic ameloblastoma with metastatic deposits

本篇報告中的病例同時具有良性與惡性之組織特徵，且沒有轉移，因此最後診斷為 ameloblastic carcinoma ex ameloblastoma。

3. 手術方式與治療過程

因為最初的切片診斷為 benign follicular ameloblastoma，因此所進行的術式為保守性切除，術後雖然發現有惡性部分，但只有局部區域且並未侵犯至手術邊緣 (surgical margin) 。傳統上， ameloblastoma 被視為一種良性腫瘤且具有局部侵犯性 (locally aggressive) ，良性腫瘤發生惡性轉變在其他位置並非罕見，因此當診斷出 ameloblastoma時，應將惡性轉變列入考慮。

4. p53 mutation

(1) 至今所確認的基因中，p53 gene 具有最高頻率會發生mutation。

(2) 作者之前的研究由 unfixed tissue 中取出 sample ，結果發現 p53 mutations 在 ameloblastoma 中不常出現(infrequent)。

(3) 在本篇報告中，不論良性或惡性區域，p53 stain 都為negative。

(4) 而針對p53 gene 的 exons 5-8 進行檢測，不論良性或惡性區均沒有發現任何 mutation (exons 5-8為p53再人類腫瘤中最易發生突變的位置)。

5. p15、p16、E-cadherin methylation

(1) 本研究觀察到在惡性區域中發現 p16 methylation ，良性區域則無 (p15 、 E-cadherin不論良性或惡性皆無)。

(2) Methylation 在tumorigenesis中扮演很重要的角色。CpG islands為methylation最常發生的位置。

(3) Oral SCC

(a) p15、p16、E-cadherin hypermethylation已在人類的oral SCC中發現。

(b) p16 tumor suppressor gene之作用—影響CDK4並抑制其kinase activity，對 cellular proliferation進行負調節。在human oral SCC，p16 inactivation常被發現 ( 因 homogenous deletion 、 mutation 與 gene hypermethylation 造成 p16 inactivation)。

(4) Ameloblastoma

(1) 與 tooth germ相較，p16、p21與p27 (inhibitors of cyclin-dependent kinase) 在 ameloblastoma中呈現well preserved，顯示odontogenic epithelium受到這些基因的調節。

(2) p16 hypermethylation 導致 p16 inactivation ，造成 deregulation of cellular proliferation。

(3) Nordit et al在ameloblastic tumor中發現allelic loss of tumor suppressor gene，

包含 p16 gene，但因為benign ameloblastoma與ameloblastic carcinoma並無顯著差異，所以他們認為其他 genetic 或 epigenetic mechanism 可能要為 ameloblastic carcinoma的惡性behavior負責。本研究支持這項結論。

- 3 -

(4)

CONCLUSION

p16基因hypermethylation的現象可能與ameloblastoma的malignant transformation有關，因為僅有一個病例，需要更多研究來證實。

題號題目

1 關於malignant amleoblastoma下列何者錯誤？

(A) 臨床上會發生轉移

(B) 顯微鏡下特徵與benign ameloblastoma相同 (C) 最常轉移的位置為肺，第二為頸部淋巴結

(D) 約1/3的病例出現轉移的時間約在primary tumor治療的5年後答案

(D)

出處：Oral and maxillofacial pathology, Neville, P.20

題號題目

2 關於ameloblastic carcinoma下列何者錯誤?

(A) 可能由ameloblastoma惡性轉變而來

(B) 顯微鏡特徵與malignant ameloblastoma 相同

(C) X光影像特徵會有ill-defined margin與cortical destruction (D) 不一定會發生轉移

答案 (B)

出處：Oral and maxillofacial pathology, Neville, P.521

- 4 -