張敏 綜述 張瑾 審校
·綜述·
三陰性乳腺癌分子分型與異質(zhì)性的研究進(jìn)展
張敏綜述張瑾審校
摘要三陰性乳腺癌(triple-negative breast cancer,TNBC)是指ER、PR及HER-2均為陰性的乳腺癌,占乳腺癌15%~20%。隨著基因組學(xué)的發(fā)展,乳腺癌的分型已不僅局限于基于免疫組織化學(xué)的傳統(tǒng)分子分型,其中TNBC也被認(rèn)為是一類(lèi)異質(zhì)性疾病,其異質(zhì)性在分子水平、病理學(xué)以及臨床特征上也各不相同。因此,對(duì)TNBC進(jìn)一步行分子分型將為靶向治療帶來(lái)極大獲益,但TNBC分子分型尚無(wú)被廣泛認(rèn)可的統(tǒng)一標(biāo)準(zhǔn),現(xiàn)就最新相關(guān)研究做一綜述。
關(guān)鍵詞三陰性乳腺癌分子分型異質(zhì)性靶向治療
雌激素受體(estrogen receptor,ER)、孕激素受體(progesterone receptor,PR)、人類(lèi)上皮生長(zhǎng)因子受體-2(human epidermal growth factor receptor-2,HER-2)均不表達(dá)的三陰性乳腺癌(triple-negative breast can?cer,TNBC)是乳腺癌研究中的熱點(diǎn)。近年來(lái)對(duì)不同亞型的TNBC是分子遺傳學(xué)上具有異質(zhì)性的疾病已有廣泛的共識(shí),但目前尚無(wú)公認(rèn)的亞型分類(lèi)。
Lehmann等[1]將TNBC從分子分型上分為6種亞型BL1(basal-like 1)和BL2(basal-like 2)基底樣亞型、免疫調(diào)節(jié)亞型、間充質(zhì)亞型、間充質(zhì)干細(xì)胞亞型、管腔雄激素受體亞型6種亞型,并且這些TNBC分子亞型表現(xiàn)出截然不同的臨床特征。Metzger-Filho等[2]對(duì)TNBC的異質(zhì)性進(jìn)行了研究,將TNBC細(xì)分為基底樣型、BRCA相關(guān)性亞型、CK和EGFR高表達(dá)亞型、Claudin-low亞型、其他病理亞型和免疫系統(tǒng)亞型6種亞型。Burstein等[3]通過(guò)基因組分析將TNBC分為腔型/雄激素受體型(luminal/androgen receptor,LAR)、間質(zhì)型(mesenchymal,MES)、基底樣/免疫抑制性(basal-like/immune-suppressed,BLIS)、基底樣/免疫激活型(basal- like/immune activated,BLIA)4個(gè)亞型。因此,“三陰性”僅僅是TNBC復(fù)雜異質(zhì)性的共同表現(xiàn),有關(guān)TNBC的異質(zhì)性及各亞型相應(yīng)的臨床、病理特征和個(gè)體化治療方法還有待進(jìn)一步研究。
2.1基底樣型乳腺癌
基底樣乳腺癌(basal-like breast cancer,BLBC)與TNBC雖然在臨床及生物學(xué)特性上有較多相同點(diǎn),但并非同義詞,兩者概念相互重疊,BLBC與TNBC重疊比例達(dá)60%~90%,TNBC中表達(dá)基底樣表型的占56%,而在非TNBC中這一比例僅為11.5%[4]。因此,TNBC與BLBC雖然并非完全等同,但密切相關(guān),臨床預(yù)后均較差,且目前尚缺乏有針對(duì)性的系統(tǒng)性治療。
BLBC的概念是基于基因表達(dá)分析,其診斷金標(biāo)準(zhǔn)為基因芯片,然而基因表達(dá)譜分析操作復(fù)雜且費(fèi)用昂貴,限制了其在臨床上的應(yīng)用。目前許多研究小組建議采用免疫組織化學(xué)檢測(cè)代替基因芯片來(lái)診斷基因組學(xué)所定義的BLBC,BLBC定義為基底細(xì)胞角蛋白(basal cytokeratins,CKs)中CK5/6和(或)CK14、CK17陽(yáng)性者[5-6]。
盡管在形態(tài)學(xué)上BLBC與非基底樣TNBC無(wú)顯著性差異,但兩者在某些免疫表型上具有顯著性差異,如低氧相關(guān)因子(CA9)、神經(jīng)內(nèi)分泌標(biāo)記、p53等。與非基底樣TNBC相比,BLBC與BRCA1突變的關(guān)系更為密切,具有獨(dú)特的遠(yuǎn)處轉(zhuǎn)移模式,且對(duì)化療更加敏感,但預(yù)后較差[7]。BLBC與BRCA1突變型乳腺癌有較多相同的生物學(xué)特性,BLBC缺乏修復(fù)停滯復(fù)制叉的能力,這也是BRCA1的功能之一,這也解釋了聚腺苷二磷酸核糖聚合酶(poly ADP-ribose polymerase,PARP)抑制劑在BLBC中無(wú)法發(fā)揮效能的原因,而鉑類(lèi)對(duì)DNA損傷喪失復(fù)制叉修復(fù)功能,可在BLBC中發(fā)揮效能[8]。
BLBC通常高表達(dá)上皮生長(zhǎng)因子受體(epidermal growth factor receptor,EGFR),最近的研究表明叉頭框C1(forkhead box C1,F(xiàn)OXC1)轉(zhuǎn)錄因子可作為BLBC的重要預(yù)后因子及功能調(diào)節(jié)因子,在BLBC中FOXC1 mRNA及其蛋白水平與EGFR的表達(dá)顯著相關(guān),同時(shí)敲降FOXC1后將減弱EGFR對(duì)BLBC細(xì)胞增殖、遷移和侵襲的影響,將給BLBC的靶向治療帶來(lái)新的方向[9]。
2.2BRCA相關(guān)亞型
BRCA基因致病性突變與乳腺癌有關(guān),與TNBC關(guān)系更為密切。BRCA1突變攜帶者的乳腺癌絕大多數(shù)(60%~80%)為T(mén)NBC[10]。BRCA1基因在乳腺癌突變的比例為4%~11%,而在TNBC中為16%~34%[11-12]。
BRCA1基因與DNA雙鏈斷裂同源重組修復(fù)有關(guān),BRCA1基因功能的缺失,將導(dǎo)致DNA雙鏈損傷修復(fù)功能的缺失,增加基因組不穩(wěn)定性。在TNBC中識(shí)別該缺陷將給臨床決策帶來(lái)決定性意義,攜帶BRCA1突變的TNBC對(duì)破壞DNA化學(xué)結(jié)構(gòu)的細(xì)胞毒性化療藥物(如烷化劑、鉑類(lèi)、絲裂霉素)和放療可能高度敏感,這為探索基于分子分型的TNBC個(gè)體化治療方案提供了理論基礎(chǔ)[13]。最近一項(xiàng)對(duì)于TNBC中BRCA1甲基化的研究發(fā)現(xiàn),BRCA1甲基化與疾病進(jìn)展相關(guān)事件的發(fā)生率降低顯著相關(guān),這表明BRCA1甲基化將帶來(lái)較好預(yù)后,同時(shí)對(duì)破壞DNA化學(xué)結(jié)構(gòu)的細(xì)胞毒性藥物敏感性較高[14]。
BLBC、TNBC和BRCA1相關(guān)性乳腺癌之間關(guān)系密切。TNBC具有BLBC和BRCA1相關(guān)性乳腺癌的大部分特征,三者相互關(guān)聯(lián),但又不能相互替代。
2.3Claudin-low亞型
Claudin-low(CL)亞型最初被Herschkowitz等[15]所定義,以間葉細(xì)胞表型為特征,低表達(dá)如緊密連接蛋白(Claudin 3、4、7)及E-鈣黏蛋白的細(xì)胞間連接蛋白,高表達(dá)如CN4及CD79a基因的免疫應(yīng)答基因,生物學(xué)觀點(diǎn)認(rèn)為CL亞型由未分化的上皮細(xì)胞組成,代表最原始的腫瘤。
與BLBC相比,CL亞型中TNBC的比例為52%,相對(duì)較低,而B(niǎo)LBC中TNBC為76%。但CL與BLBC相似,均表現(xiàn)出較高的基因組不穩(wěn)定性,存在大量的基因擴(kuò)增或缺失。在轉(zhuǎn)錄水平上CL是低分化甚至未分化的類(lèi)型,高表達(dá)上皮間質(zhì)轉(zhuǎn)化(epithelial-mesen?chymal transition,EMT)相關(guān)分子學(xué)標(biāo)記、免疫應(yīng)答基因以及腫瘤干細(xì)胞樣特征[16]。
對(duì)于CL亞型乳腺癌發(fā)生機(jī)制及影響因子的探索也是近年的研究熱點(diǎn)。近期有研究發(fā)現(xiàn),STAT3在CL亞型乳腺癌的腫瘤干細(xì)胞中首先被激活,導(dǎo)致腫瘤的發(fā)生發(fā)展,因而針對(duì)STAT3的靶向治療將給CL亞型乳腺癌患者帶來(lái)獲益[17]。另有研究報(bào)道,利用p53缺失的轉(zhuǎn)基因小鼠模型,使其高表達(dá)催乳素,發(fā)現(xiàn)在p53缺失的情況下,催乳素將縮短乳腺癌發(fā)生的潛伏期,同時(shí)三陰性CL亞型腫瘤的比例明顯升高,這表明催乳素與p53缺失共同作用促進(jìn)了三陰性CL亞型腫瘤的發(fā)生[18]。
2.4CK和EGFR高表達(dá)亞型
EGFR的高表達(dá)在大多數(shù)TNBC的發(fā)生發(fā)展中起重要作用。Corkery等[19]研究認(rèn)為,與HER-2陽(yáng)性細(xì)胞系相比,EGFR在TNBC中表達(dá)水平更高,并且經(jīng)上皮生長(zhǎng)因子作用后可發(fā)現(xiàn)TNBC細(xì)胞系中EGFR的磷酸化。該研究中EGFR的磷酸化可導(dǎo)致包括MEK/ ERK和PI3K/Akt通路在內(nèi)的下游信號(hào)轉(zhuǎn)導(dǎo)通路的激活,引起相關(guān)基因的表達(dá),從而抑制腫瘤細(xì)胞凋亡,促進(jìn)腫瘤細(xì)胞增殖、轉(zhuǎn)移及血管生成,促進(jìn)腫瘤發(fā)展。因此,EGFR信號(hào)通路在TNBC的發(fā)生發(fā)展中可能起關(guān)鍵作用,并可能作為T(mén)NBC治療的靶點(diǎn)。
45%~70% TNBC存在EGFR基因高表達(dá)或擴(kuò)增,因此TNBC最有可能從抗EGFR治療中獲益。EGFR的單克隆抗體西妥昔單抗在TNBC的細(xì)胞實(shí)驗(yàn)中亦觀察到具有一定的作用效果。乳腺癌轉(zhuǎn)化治療研究聯(lián)盟(TBCRC)001多中心臨床研究顯示,102例TNBC轉(zhuǎn)移性患者,西妥昔單抗聯(lián)合卡鉑治療組有效率為17%,中位PFS僅2個(gè)月,提示預(yù)后兇險(xiǎn)[20]。美國(guó)腫瘤組的一項(xiàng)Ⅱ期臨床試驗(yàn)研究顯示,在TNBC亞組中伊立替康+卡鉑治療組與伊立替康+卡鉑+西妥昔單抗治療組客觀有效率分別為30%與49%[21]??傊?,雖然西妥昔單抗治療TNBC具有一定療效,但其療效仍令人失望,因此對(duì)其敏感的TNBC亞群患者進(jìn)行個(gè)體化治療顯得至關(guān)重要。
2.5免疫系統(tǒng)亞型
最近,一項(xiàng)通過(guò)對(duì)2 100例乳腺癌患者的薈萃分析發(fā)現(xiàn),對(duì)腫瘤侵犯、免疫應(yīng)答、血管生成、凋亡及增殖等相關(guān)基因表達(dá)與乳腺癌預(yù)后相關(guān)性的評(píng)估中,TNBC只有免疫應(yīng)答基因高表達(dá)與較好的預(yù)后顯著相關(guān),其他基因改變并非其獨(dú)立預(yù)后因素[22]。最近的臨床研究證實(shí),腫瘤組織中淋巴細(xì)胞浸潤(rùn)(tumorinfiltrating lymphocytes,TILs)是TNBC的獨(dú)立預(yù)后因素,TILs者預(yù)后較好,TILs每增加10%,局部復(fù)發(fā)風(fēng)險(xiǎn)降低14%(P=0.02),遠(yuǎn)處轉(zhuǎn)移風(fēng)險(xiǎn)降低18%(P= 0.04),死亡風(fēng)險(xiǎn)降低19%(P=0.01)[23]。但有研究認(rèn)為免疫特性是免疫系統(tǒng)亞型癌細(xì)胞本身所具有的特性,與免疫細(xì)胞浸潤(rùn)的多少無(wú)關(guān)[3]。除淋巴細(xì)胞外,NK細(xì)胞在TNBC中具有細(xì)胞溶解作用,且與ER陽(yáng)性乳腺癌相比,TNBC中NK細(xì)胞的作用明顯增強(qiáng),因此免疫調(diào)節(jié)治療對(duì)于TNBC患者的治療顯得更為重要[24]。
目前,對(duì)于TNBC藥物治療策略的探索大多集中于研制新的細(xì)胞毒性藥物或應(yīng)用現(xiàn)有細(xì)胞毒性藥物聯(lián)合分子靶向制劑,免疫治療的出現(xiàn)將給TNBC患者帶來(lái)新的希望。
2.6腔型/雄激素受體型
腔型/雄激素受體型是分化程度最高的乳腺癌亞型,該亞型不表達(dá)TNBC傳統(tǒng)常見(jiàn)的基底樣型,而是表達(dá)Luminal型上皮的細(xì)胞特征、并且雄激素受體(androgen receptor,AR)陽(yáng)性[3]。這一TNBC亞型可能通過(guò)AR通路激活腫瘤生長(zhǎng),故AR有可能成為其治療靶點(diǎn)。
目前,AR已成為T(mén)NBC的研究熱點(diǎn),為探索TN?BC更為有效的治療靶點(diǎn)提供了新的方向。AR抑制劑比卡魯胺在TNBC某些亞型中被證實(shí)具有較好的臨床療效[25]。MDV3100-11研究評(píng)估單藥雄激素受體抑制劑恩雜魯胺用于晚期雄激素受體陽(yáng)性的TN?BC患者的Ⅱ期臨床試驗(yàn)研究顯示,79%患者有AR表達(dá),55%患者AR表達(dá)≥10%,AR在TNBC中的表達(dá)普遍高于之前的報(bào)道,雄激素基因檢測(cè)陽(yáng)性(Dx+)者的中位PFS為32周,陰性者(Dx-)為9周,雄激素基因檢測(cè)陽(yáng)性者臨床治療效果更為顯著[26]。
TNBC是一類(lèi)高度異質(zhì)性的疾病,目前對(duì)其分子分型暫無(wú)廣泛共識(shí),是乳腺癌研究的熱點(diǎn)。基因分子生物學(xué)的飛速發(fā)展為探索TNBC分子分型和異質(zhì)性帶來(lái)了廣闊前景。針對(duì)TNBC基因組、分子標(biāo)記物以及生物學(xué)行為研究的不斷深入,將有助于理解該型乳腺癌的復(fù)雜性,鑒別其異質(zhì)性,從分子生物學(xué)角度系統(tǒng)地對(duì)TNBC進(jìn)行合理的分子分型,為T(mén)NBC規(guī)范化、個(gè)體化精準(zhǔn)診療帶來(lái)新的思路。
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(2016-01-28收稿)
(2016-03-18修回)
Research progress on molecular classification and heterogeneity of triple- negative breast cancer
Min ZHANG, Jin ZHANG
Correspondence to: Jin ZHANG; E-mail: zhangjin@tjmuch.com
The Third Department of Breast Cancer, Tianjin Medical University Cancer Institute and Hospital, Tianjin Breast Cancer Prevention, Treatment, and Research Center; National Clinical Research Center for Cancer; Key Laboratory of Breast Cancer Prevention and Therapy of Ministry of Education; Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin 300060, China
AbstractTriple-negative breast cancer (TNBC) is defined by the lack of estrogen receptors (ERs) and progesterone receptors (PRs) and by the human epidermal growth factor receptor 2 (HER2)-negative status. TNBC accounts for 15% to 20% of breast cancer cases. Genomic profiling studies have demonstrated that breast cancer heterogeneity extends beyond the classic immunohistochemistry (IHC)-based divisions. TNBC is also a heterogeneous disease on the molecular level, as well as on the pathologic and clinical levels. Thus, the molecular subclassification of TNBC will be of considerable value to the development of targeted therapies. However, no widely recognized standard for the molecular classification of TNBC exists. This review provides a brief summary on the latest research on TNBC.
Keywords:triple-negative breast cancer, molecular subtypes, heterogeneity, targeted therapy
doi:10.3969/j.issn.1000-8179.2016.07.105
作者單位:天津醫(yī)科大學(xué)腫瘤醫(yī)院乳腺腫瘤三科,國(guó)家腫瘤臨床醫(yī)學(xué)研究中心,中國(guó)天津乳腺癌防治研究中心,天津市腫瘤防治重點(diǎn)實(shí)驗(yàn)室,乳腺癌防治教育部重點(diǎn)實(shí)驗(yàn)室(天津市300060)
通信作者:張瑾zhangjin@tjmuch.com.cn
作者簡(jiǎn)介
張敏專(zhuān)業(yè)方向?yàn)槿橄侔┚珳?zhǔn)醫(yī)療及新輔助治療的研究。
E-mail:maxine_zhang@126.com