頭頸癌生物標志物研究進展

付立偉，張小濤，田永峰，胡清源(綜述)，陳 歡，侯宏衛(wèi)(審校)

(國家煙草質量監(jiān)督檢驗中心，鄭州 450001)

頭頸部腫瘤包括除眼、腦、耳、甲狀腺以及食管外的頭頸部組織或器官的腫瘤，超過90%的頭頸部腫瘤為鱗狀細胞癌[1]。由于缺乏有效的早期檢測和風險評估手段，超過50%的頭頸癌患者確診時已屬晚期，盡管化療、放療等手段可在一定程度上緩解病情，但5年生存期仍低于50%[2]。全球每年約有60萬例新發(fā)頭頸部腫瘤病例，其中30多萬例死亡[3]。

頭頸部腫瘤的主要誘因是煙草、酒精和人類乳頭瘤病毒(human papillomavirus，HPV)[4]，煙草是頭頸癌最主要的誘因。流行病學研究表明，至少75%的頭頸癌患者有吸煙和(或)飲酒史；頭頸癌吸煙患者病死率較戒煙或非吸煙患者高4倍[5]。飲酒是頭頸癌的第二大誘因，每日飲酒量>50 g，患癌風險率提高5.5%，但適度飲酒(每日10～19 g)不會增加患頭頸癌的風險[6]。HPV是除吸煙、飲酒外的頭頸癌的另一大誘因，因HPV感染而形成的口咽鱗狀細胞癌正逐年增多，超過50%的口咽癌與HPV感染有關[7]。HPV呈陽性的頭頸癌患者與其他頭頸癌患者相比呈現(xiàn)年輕化，其煙酒攝入量少，有相對更多的性伴侶[8]。

在頭頸部腫瘤形成初期，淋巴結轉移較少，對腫瘤的治療也最為有效，然而大約2/3的頭頸部腫瘤患者確診時已屬晚期[9]，因此早期確診對于改善患者的存活率有重要意義。目前由于缺乏有效的早期診斷的生物標志物，頭頸癌的早期篩查和發(fā)現(xiàn)仍然是難題，頭頸癌生物標志物的深入研究將為今后改善頭頸癌的早期診斷、分級、復發(fā)及預后評估提供可能性。

1 DNA甲基化

DNA甲基化過程可使甲基添加到DNA分子上，其能夠在不改變DNA序列的前提下，改變遺傳表現(xiàn)。DNA甲基化早于細胞的惡性增生，DNA甲基化的診斷對于腫瘤早期預測有重要意義。目前發(fā)現(xiàn)的與頭頸部腫瘤相關的甲基化基因包括：p16、p15、p14、死亡相關蛋白激酶、6-氧甲基鳥嘌呤-DNA甲基轉移酶、鈣黏蛋白等(表1)。Carvalho等[10]采用甲基化特異聚合酶鏈反應(methylation specific polymerase chain reaction，MSP)檢測大量頭頸癌患者的血清和唾液樣本發(fā)現(xiàn)其特異度高達90%；Sanchez-Cespedes等[11]通過檢測頭頸癌患者腫瘤組織和唾液中p16、6-氧甲基鳥嘌呤-DNA甲基轉移酶、死亡相關蛋白激酶的甲基化發(fā)現(xiàn)，在腫瘤組織不同病理分化階段均存在DNA甲基化，對于口腔部位的腫瘤，唾液中DNA甲基化率相對較高，而在腫瘤組織中未發(fā)現(xiàn)DNA甲基化的患者其相應的唾液樣本中也未出現(xiàn)甲基化現(xiàn)象[11]。對于做過腫瘤切除手術的頭頸部腫瘤患者，采用MSP檢測其唾液樣本中DNA甲基化率對其病情監(jiān)測有一定的臨床應用前景。

Chang等[12]研究發(fā)現(xiàn)，頭頸癌患者體液和腫瘤組織中p15、p16甲基化程度明顯高于健康對照組，有長期吸煙或飲酒習慣的頭頸癌患者腫瘤組織中p15的甲基化程度高于頭頸癌非吸煙患者。有研究認為，煙草暴露可能會造成CpG島的特異性損害或降低DNA甲基轉移酶的活性[13]。

表1 頭頸部腫瘤相關基因甲基化

CYP1A1：細胞色素P450酶；CYP2AI3：細胞色素P450酶；GSTMI：谷胱甘肽轉移酶M1；EDNRB：內皮素B受體；KIF1A：微管驅動蛋白家族成員1A；CDKN：周期蛋白依賴性蛋白激酶抑制劑；RUNX3：RUNT相關轉錄因子3；SFN：人分層蛋白基因；MSP：甲基化特異聚合酶鏈反應

2 基質金屬蛋白酶

基質金屬蛋白酶(matrix metalloproteinases，MMPs)幾乎能降解細胞外基質中所有的蛋白成分，能降解破壞腫瘤細胞侵襲、轉移所需要越過的組織學屏障，在腫瘤侵襲轉移中起關鍵作用[20]。研究發(fā)現(xiàn)，頭頸癌者體內易出現(xiàn)MMPs過表達現(xiàn)象。Ruokolainen等[21]通過比較頭頸癌患者與健康人群血清中MMP-9的水平發(fā)現(xiàn)，MMP-9水平偏高的頭頸癌患者相比其他患者死亡風險更高，并認為MMP-9有希望成為頭頸癌診斷的生物標志物。Kuropkat等[22]研究發(fā)現(xiàn)，頭頸癌患者血清中MMP-3、MMP-8、MMP-9的水平明顯高于健康人群，其中血清中MMP-8的水平與腫瘤所處的階段相關。Kawata等[23]發(fā)現(xiàn)，正常黏膜與腫瘤組織中MMP-2的水平無明顯差異，但出現(xiàn)淋巴結轉移的腫瘤組織其MMP-2水平明顯高于未發(fā)生轉移者。其他研究也發(fā)現(xiàn)，MMP-2和MMP-14的過表達與頭頸癌淋巴結轉移有關，其對于頭頸癌的預后有重要價值[24]。與頭頸部腫瘤相關的標志物包括MMPs、Ki-67、人類表皮生長因子受體2等(表2)。

表2 與頭頸部腫瘤相關的MMPs

MMP：基質金屬蛋白酶；TIMP-1：基質金屬蛋白酶組織抑制因子；HER-2：人類表皮生長因子受體2；

3 細胞因子

細胞因子是調節(jié)炎癥與血管生成的重要蛋白質，目前已被廣泛認可的與頭頸癌檢測、預后以及監(jiān)控有關的細胞因子包括血管內皮生長因子(vascular endothelial growth factor，VEGF)[31]、白細胞介素6(interleukin-6，IL-6)等(表3)。

Chen等[32]檢測出頭頸癌患者唾液中IL-6、IL-8和VEGF的水平高于健康人群。Mineta等[33]將12項關于VEGF過表達與頭頸癌存活率的數(shù)據(jù)進行統(tǒng)計學分析表明，VEGF陽性患者2年內死亡的風險率提高1.88倍，VEGF過表達對頭頸癌淋巴結轉移有預測價值。Akmansu等[34]對放射治療前后頭頸癌患者唾液中IL-6的水平進行檢測發(fā)現(xiàn)，放射治療后患者唾液中IL-6的水平明顯升高。Duffy等[35]認為，IL-6是預測癌癥復發(fā)及存活率的獨立的生物標志物，其對于頭頸癌的診斷和治療有重要意義。Gokhale等[36]發(fā)現(xiàn)，唾液中IL-8的水平在頭頸癌復發(fā)和轉移階段明顯高于頭頸癌形成初期，其對頭頸癌的預后有重要意義。Korostoff等[37]采用定量酶聯(lián)免疫吸附法檢測喉鱗癌患者和對照組唾液中多種細胞因子的水平發(fā)現(xiàn)，外生性喉鱗癌患者唾液中IL-8的水平明顯高于健康對照組。唾液及血清中IL-6和IL-8的測定通常采用酶聯(lián)免疫吸附法，其敏感性和特異性較好，且操作簡便、快速。IL-6、IL-8和VEGF等細胞因子對于頭頸癌的分級和預后有重要研究價值。

表3 頭頸部腫瘤相關細胞因子

VEGF：血管內皮生長因子；IL：白細胞介素；HGF：肝細胞生長因子；MMP：基質金屬蛋白酶；TNF：腫瘤壞死因子

4 小 結

p16基因甲基化、MMP家族成員、IL-6、IL-8等生物標志物已被證明在頭頸癌患者體液和組織中存在異常表達。這些生物標志物的發(fā)現(xiàn)為今后改善頭頸癌早期診斷、分級以及預后等方面有重要意義。但頭頸癌生物標志物真正的應用于臨床還有較長的路要走，且臨床診斷要求標志物分析過程準確、簡單及標準化，多數(shù)生物標志物仍然需要進一步的研究以提供準確而規(guī)范標準化的分析流程。

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