海军军医大学学报  2023, Vol. 44 Issue (1): 80-90   PDF    
肝细胞癌的血液检测指标研究进展
范浙才1,2, 杨钊3     
1. 海军军医大学(第二军医大学)国家肝癌科学中心医学转化研究室, 上海 201805;
2. 海军军医大学(第二军医大学)第三附属医院国际合作生物信号转导研究室, 上海 200438;
3. 海军军医大学(第二军医大学)第三附属医院肝外二科, 上海 200438
摘要: 原发性肝癌是我国最常见的恶性肿瘤之一,病死率高,其主要病理类型为肝细胞癌。大多肝细胞癌患者在初诊时已是晚期,5年生存率低于16%,实现肝癌的早发现和早诊断有助于改善患者的预后。血液检测具有微创、客观、经济、可重复和可动态监测的优点,可用于肝细胞癌高危人群的筛查和辅助诊断。本文回顾了已有报道的肝细胞癌血液检测指标,分为血清中可直接检出的标志物、细胞外囊泡中的标志物及循环肿瘤细胞中的标志物3类,阐述其优势及局限性,并对未来肝癌早期筛查的血液学检测新策略进行展望。
关键词: 肝肿瘤    肝细胞癌    肿瘤生物标志物    筛查    早期诊断    
Blood test indicators for hepatocellular carcinoma: research progress
FAN Zhe-cai1,2, YANG Zhao3     
1. Department of Medical Transcription, National Center for Liver Cancer, Naval Medical University (Second Military Medical University), Shanghai 201805, China;
2. International Cooperation Laboratory on Signal Transduction, The Third Affiliated Hospital of Naval Medical University (Second Military Medical University), Shanghai 200438, China;
3. Department of Hepatic Surgery (Ⅱ), The Third Affiliated Hospital of Naval Medical University (Second Military Medical University), Shanghai 200438, China
Abstract: Primary liver cancer is one of the most common malignant tumors in China, with high incidence and mortality, and the main pathological type is hepatocellular carcinoma (HCC). Most patients with HCC are already at the advanced stages at the first diagnosis, with the 5-year survival rate being less than 16%. Early detection and early diagnosis of liver cancer can help improve the prognosis of patients. Blood testing is commonly used to screen patients with high risks of liver cancer because it is minimally invasive, objective, economical, repeatable and easy to monitored. This article summarized 3 types of reported indicators for blood screening of liver cancer: biomarkers that could be directly detected in the serum, biomarkers in the cargoes transferred by extracellular vesicles, and biomarkers in circulating tumor cells. The advantages and limitations of each category were discussed. We also provided perspectives for the promising strategies of blood testing for HCC screening and diagnosis in future.
Key words: liver neoplasms    hepatocellular carcinoma    tumor biomarkers    screening    early diagnosis    

原发性肝癌是全球第六大常见肿瘤和第三大肿瘤相关死亡的病因[1],也是我国发病率和死亡率较高的恶性肿瘤,严重威胁人类生命和健康[2]。肝细胞癌(hepatocellular carcinoma,HCC)是原发性肝癌的主要病理类型,约占75%~85%[3]。HCC起病隐匿、进展迅速、恶性程度高,早期诊断困难,大部分病例在初诊时已为晚期,采用手术等干预治疗效果较差[4-5]。晚期HCC患者5年生存率低于16%,而早期HCC患者5年生存率高于70%[6]。因此,高效的早期检测和诊断方法对于HCC患者的治疗和预后至关重要。

HCC的高危因素主要包括HBV感染、丙型肝炎病毒感染、长期酗酒、肝硬化、非酒精性脂肪性肝病(nonalcoholic fatty liver disease,NAFLD)等[7],其中NAFLD正成为发达地区HCC的主要原因[8-9]。目前,超声检查是HCC监测的常用方法,但其准确度高度依赖于操作者的熟练程度,临床诊断的成功率低于预期值。血清肿瘤标志物的检测具有微创、客观、可重复及可动态监测的优点,是HCC监测和早期诊断的重要方法,其中甲胎蛋白(α-fetoprotein,AFP)是临床常用的HCC血清学标志物,但灵敏度不高。我国《原发性肝癌诊疗指南(2022年版)》建议高风险人群每6个月进行一次超声联合血清AFP检测来监测HCC的发生风险[2]。随着分子生物学和生物信息学技术的进步,越来越多的HCC血清学标志物被发现。本文回顾了已报道的HCC血液学检测指标,分为血清中直接可检出的标志物、细胞外囊泡为载体的标志物及循环肿瘤细胞中的标志物3类,对其研究进展进行综述。

1 血清中直接可检出的标志物 1.1 蛋白类标志物

AFP是一种单链糖蛋白,在临床上广泛应用于HCC的辅助诊断和预后评估。AFP诊断HCC的灵敏度为60%,特异度为90%[10]。但AFP在30%~40%的HCC患者血清中呈阴性(<20 ng/mL),且在急慢性肝炎、肝硬化等良性肝病患者中呈现不同程度的升高[11]。AFP除了作为HCC的诊断标志物外,还具有多种生物学功能,在诱导肝细胞恶性转化及调节细胞增殖、迁移、凋亡和免疫逃逸等方面发挥重要作用[12]。高水平血清AFP通常意味着HCC的进展风险和不良预后[13]

根据与小扁豆凝集素(lens culinaris agglutinin,LCA)的亲和力,AFP可分为3种类型:AFP-L1、AFP-L2、AFP-L3[14]。其中AFP-L3主要来源于肝癌细胞。临床以血清中AFP-L3占总AFP的比例(AFP-L3%)作为肝癌的诊断指标(临界值为10%),其特异度高达95%,灵敏度为51%[15]。AFP-L3的灵敏度与HCC临床分期相关,在小HCC(直径≤2 cm)中AFP-L3的灵敏度约为35%~45%,而当肿瘤直径增大(≥5 cm)时其灵敏度可达80%~90%[16]。由于AFP-L3的灵敏度相对较低,通常与AFP联用作为HCC的辅助诊断标志物。

脱-γ-羧基凝血酶原(des-γ-carboxy prothrombin,DCP)又称维生素K缺乏或拮抗剂-Ⅱ诱导的蛋白质(protein induced by vitamin K absence or antagonist-Ⅱ,PIVKA-Ⅱ),在维生素K缺乏或HCC患者的血清中升高。国内的一项大样本多中心研究发现,在HBV相关HCC患者中,DCP(临界值40 mAU/mL)准确度高于AFP[14]。另外,DCP与AFP无相关性,两者对诊断HCC具有互补性,AFP和DCP联合诊断HCC准确度高于单独使用DCP或AFP[17]

其他蛋白类标志物如骨桥蛋白(osteopontin,OPN)[18]、高尔基蛋白73(Golgi protein 73,GP73)[19]、α-1-岩藻糖苷酶(α-1-fucosidase,AFU)[20]等在早期HCC的诊断上有一定价值。

1.2 糖类标志物

随着目前糖生物学、糖蛋白质组学及糖组学研究技术的不断深入,糖基化异常与HCC的关系受到越来越多的关注。Liu等[21]对临床不同分级的肝纤维化、HCC患者的血清N-聚糖图谱进行比较,结果显示在肝硬化患者中筛查HCC时,GlycoHCCTest(三半乳糖-α-1, 3-分支岩藻糖基化三天线结构/双半乳糖-α-1, 6-核心岩藻糖基化平分型二天线结构比值的对数值)与AFP具有相似的灵敏度与特异度。同时在相关糖组学的研究中还发现,血清IgG来源的N-糖链对AFP阴性的HCC患者具有重要的补充诊断价值。以上研究表明部分糖蛋白糖基化产物在HCC的诊断中具有重要的参考价值[22]

1.3 联合生物标志物及相关数学模型

单一血清学检测指标在诊断早期HCC的临床应用中经常存在漏诊和误诊的情况,联合使用多个血清学检测指标或可提高HCC的检出率,例如国际上应用较为广泛的肝癌三联检就是联合检测AFP、AFP-L3%和DCP[23],而联合检测AFP、丙氨酸转氨酶(alanine aminotransferase,ALT)、天冬氨酸转氨酶(aspartate aminotransferase,AST)和中性粒细胞与淋巴细胞比值(neutrophil-lymphocyte ratio,NLR)有助于HBV相关HCC的诊断[24]。Best等[25]基于临床数据和血清肿瘤标志物构建了GALAD评分系统,其公式为GALAD=-10.08+0.09×年龄+1.67×性别+2.34×lg AFP+0.04×AFP-L3+1.33×lg DCP,公式中的性别为男取值1、女取值0;当GALAD评分临界值定为-0.63时,诊断HCC的灵敏度为68.0%、特异度为95.0%,其AUC高于超声检查。然而,该队列样本中非病毒性感染是早期HCC的主要致病因素,而我国大部分HCC患者主要是由于HBV感染造成肝硬化最终演变而来,GALAD评分系统不一定适用于HBV感染为主要风险因素的HCC患者。在该评分系统的基础上,国内研究团队建立了基于病毒感染相关HCC为主的GALAD-C评分系统。GALAD-C=-11.501+0.099×年龄+0.733×性别+0.840×lg AFP+0.073×AFP-L3%+2.364×lg DCP,公式中的性别为男取值1、女取值0;该模型预测病毒感染HCC的灵敏度和特异度分别为82.60%和85.90%[26]。GALAD、GALAD-C等评分系统有助于早期HCC的筛查和诊断,但其临床价值仍需大规模队列研究进一步验证。血清中直接可检出的肝癌诊断相关蛋白标志物及多参数模型见表 1

表 1 血清中直接可检出的HCC诊断相关蛋白标志物及多参数模型 Tab 1 Directly detectable protein markers for HCC diagnosis in serum and multi-parameter model

1.4 miRNA

miRNA是一类由内源基因编码的长度约为22个核苷酸的非编码单链RNA分子。随着液体活检技术的发展,越来越多的研究发现在患者体液(包括血清、唾液、尿液和粪便等)中存在大量的miRNA[27],且其表达具有一定的稳定性[28]。血清中可检出多种miRNA,其水平与肝病进展密切相关[27, 29-31]。肝脏来源的miRNA可能通过细胞凋亡和坏死被动进入血清或通过外泌体和病毒颗粒的分泌主动进入血清[32],而检测血清miRNA的创伤性远小于组织活检,因此,以血清中miRNA水平评估肝脏中miRNA水平是较有推广前景的检测手段。

研究表明,循环miRNA-21水平升高可用来区分HCC与慢性肝炎(灵敏度和特异度分别为61.1%和83.3%)及HCC与健康对照样本(灵敏度和特异度分别为87.3%和92.0%),ROC曲线分析显示miRNA-21预测HCC的AUC为0.773,预测HCC的效能优于AFP[33]。此外,HCC患者血清中miRNA-15b和miRNA-130b的表达也显著上调[34],miRNA-130b在检测HCC中的AUC为0.913,灵敏度和特异度分别为87.7%和81.4%;相比之下,虽然miRNA-15b检测HCC的灵敏度高达98.3%,但其特异度却仅为15.3%。血清miRNA-15b和miRNA-130b的高灵敏度提示两者可以作为AFP水平较低的早期HCC患者筛查和预警的生物标志物。

国内研究人员开展了一项包括7个医学中心的回顾性研究,通过严格的筛选标准从9 287例慢性乙型肝炎患者中筛选出195例临床前患者(确诊HCC前平均6个月采集的样本)和435例慢性乙型肝炎患者,并从血清中鉴定出一组miRNA(miRNA-193a-3p、miRNA-369-5p、miRNA-672、miRNA-429、let-7i*),该组血清miRNA可用于预测慢性乙型肝炎患者进展为HCC的风险[35]。此外,在HBV相关早期HCC(巴塞罗那分期0期和A期)的诊断中,一组7种miRNA的组合(miRNA-122、miRNA-192、miRNA-21、miRNA-223、miRNA-26a、miRNA-27a和miRNA-801)也被证明具有较高的准确性,AUC可达到0.888[36]

1.5 长链非编码RNA(long non-coding RNA,lncRNA)

lncRNA是一种长度超过200个核苷酸的非编码RNA。研究发现,与正常肝组织相比多种lncRNA在HCC中异常表达,比如LINC00794[37]、lncRNA SPRY4-IT1[38]、lncRNA MALAT[39]等。但是,部分lncRNA在其他癌症或非癌肝损伤中也异常表达。因此,lncRNA与其他分子尤其是已知的HCC生物标志物联用,可能是一种更理想的HCC诊断方法。例如,lncRNA UCA1和lncRNA WRAP53与AFP的组合实现了高达100%的灵敏度[40]。类似地,另外2种lncRNA人浆细胞瘤转化迁移基因1(plasmacytoma variant translocation 1,PVT1)和lncRNA uc002mbe.2与AFP的组合也比单独使用AFP效果更好[41]。另外,研究发现循环血中3种lncRNA(LINC00152、RP11-160H22.5和XLOC014172)与AFP联合检测可预测肝硬化患者和健康受试者向HCC进展的潜在风险[42]

除了诊断价值外,lncRNA也可作为HCC的潜在预后标志物。例如,lncRNA WRAP53也是一种独立的预后标志物,可预测HCC患者的高复发率[40]。lncRNA-ATB上调提示HCC患者肿瘤易发生转移,且往往预后不良[43];相反,具有转移抑制功能的lncRNA miR503HG上调则是一个有利的预后指标[44]

1.6 环状RNA(circular RNA,circRNA)

circRNA是缺乏5'和3'末端的内源性非编码RNA,是前体mRNA反向剪接的产物[45]。circRNA的环状结构使其不受RNA酶影响,表达稳定且不易降解。circRNA序列中存在特定的miRNA结合位点,可调控miRNA的表达,因此,circRNA的异常表达也可介导肿瘤的进展。由于其高稳定性和丰度,体液中的circRNA被认为是很有前景的液体活检生物标志物[46]

通过临床样本的检测发现,circRNA CDYL在肝癌早期特异性升高,并显著促进了上皮细胞黏附分子(epithelial cell adhesion molecule,EpCAM)阳性的肝癌起始细胞的形成。circRNA CDYL通过竞争性结合miRNA-892a和miRNA-328-3p,分别与调节肝癌来源生长因子(hepatoma-derived growth factor,HDGF)和低氧诱导因子天冬酰胺羟化酶(hypoxia-inducible factor asparagine hydroxylase,HIF1AN)的mRNA形成相互作用网络。因此,circRNA CDYL或circRNA CDYL联合HDGF和HIF1AN均可作为HCC诊断的标志物[47]。另有研究分析了exoRBase数据库中HCC和正常人血液样本的circRNA表达谱,认为hsa_circ_0004001、hsa_circ_0004123、hsa_circ_0075792及三者的组合在HCC的诊断中具有潜在价值[48]。血清中直接可检出的肝癌诊断或进展核酸类标志物见表 2

表 2 血清中直接可检出的HCC诊断或进展核酸类标志物 Tab 2 Directly detectable nucleic acid markers for diagnosis or progression of HCC in serum

综上所述,蛋白类血清生物标志物是目前推广应用最为广泛的诊断标志物,对HCC的早期诊断起到辅助作用,由于单个标志物的诊断效能往往受到多方面因素的限制,因此研究人员将多个生物标志物联合应用诊断HCC,但其效能还需要进一步的多中心大样本验证;miRNA、lncRNA和circRNA是当前血清中可直接检出生物标志物研究的新方向,与HCC的进展密切相关,该类标志物的稳定性及预测HCC的效能也还有待进一步验证。

2 细胞外囊泡为载体的生物标志物

细胞外囊泡是指从细胞膜上脱落或由细胞分泌的双层膜结构的囊泡状小体,包括外泌体和微囊泡。有研究表明细胞外囊泡携带着一系列具有生物活性的物质,如可溶性蛋白、膜结合蛋白、脂质、代谢物、DNA和RNA[49],且与供体细胞相比细胞外囊泡中的内容物通常更加富集、浓度较高、更易检出[50]。同时,以液体活检的方式检测血液中细胞外囊泡可以减少对病患的侵入性伤害,因此,细胞外囊泡运输的核酸及蛋白具有作为HCC生物标志物的潜在价值。

2.1 外泌体为载体的生物标志物

外泌体是一种直径约30~150 nm的圆盘状或杯状细胞外囊泡,其内富含RNA、蛋白质等。近期研究发现,相比于慢性肝炎或非HCC患者,HCC患者外泌体中miRNA-21-5p、miRNA-10b-5p、miRNA-221-3p和miRNA-223-3p上调[51];另有研究表明HCC患者血清外泌体中miRNA-18a、miRNA-221、miRNA-222和miRNA-224水平升高,而miRNA-101、miRNA-106b、miRNA-122、miRNA-195和miRNA-125b水平下降[52-53];另外来源于外泌体的LINC00161在HCC患者的血清样本中上调,且结果具有稳定性和特异性[54]。这些结果提示循环外泌体miRNA和lncRNA可用于辅助诊断HCC,尤其可以作为AFP阴性的HCC患者早期预警指标[51]。此外,在肝移植术后复发HCC患者的血清中检测到外泌体中抑癌基因miRNA-718显著低于未复发患者[55],血清外泌体中miRNA-1247-3p表达水平与HCC的转移相关[56],以上研究表明循环外泌体miRNA可用于预测肿瘤复发或转移。

除了miRNA,HCC患者血清外泌体中运载的蛋白质也可提示肝癌进展。研究发现,半乳糖凝集素3结合蛋白(galectin-3-binding protein,LG3BP)和聚合免疫球蛋白受体(polymeric immunoglobulin receptor,PIGR)在HCC患者中高表达,二者联合使用可预测HCC的发生,AUC值高于AFP[57]。此外,HCC患者外周血中存在富含SMAD家族成员3(SMAD family member 3,SMAD3)的外泌体,其水平与HCC患者的疾病分期和病理分级密切相关[58]。另一项研究表明,高转移性细胞分泌的外泌体中腺苷酸环化酶相关蛋白1(adenylyl cyclase-associated protein 1,CAP1)显著富集,其与HCC转移和复发有一定的关联[59]

2.2 微囊泡为载体的生物标志物

微囊泡是一种直径为100~1 000 nm的细胞外囊泡,由质膜出芽形成,其内包含部分细胞质[60],由于其直径大于外泌体,常作为大分子蛋白质载体发挥作用。目前已有一些研究探究了微囊泡中的蛋白质作为HCC诊断和预后指标的可能性。例如,HCC患者的血浆微囊泡M2型丙酮酸激酶(pyruvate kinase M2,PKM2)的水平显著高于健康人,与HCC发生呈正相关[61]。肝移植术后早期复发的HCC患者中HepPar1+微囊泡的数量显著高于未复发的患者,或可用于预测HCC患者预后[62]。近期发表的一项研究评估了肿瘤相关微粒(tumor-associated microparticle,taMP)用于HCC和胆管癌检测和监测的价值。研究发现,在HCC和胆管癌中膜联蛋白Ⅴ(annexinⅤ)+ EpCAM+ CD147+ taMP显著升高,同时,annexinⅤ+ EpCAM+去唾液酸糖蛋白受体1(monoclonal antibody to asialoglycoprotein receptor 1,ASGPR1)+ CD133+ taMP可用于鉴别肝脏恶性肿瘤患者(HCC和胆管癌)、肝硬化患者和非肝癌肿瘤患者。相比肝硬化患者,肝癌患者的annexinⅤ+ EpCAM+ ASGPR1+ taMP显著增加,其水平在肝癌根治术后7 d内下降,这一发现表明该taMP与肿瘤形成密切相关[63]。除了囊泡表面标志物的变化外,taMP浓度变化也可用于评估HCC的发生和进展程度。HCC患者外周血微囊泡水平显著高于肝硬化患者,且与HCC肿瘤大小、病理类型和TNM分期相关[64]。综上所述,细胞外囊泡的血浆水平变化及其作为载体传递的核酸及蛋白均可为肝癌的诊断及预后提供一定的参考,具有作为肝癌潜在诊断和预后生物标志物的可能性(表 3)。

表 3 细胞外囊泡为载体的HCC诊断或预后标志物 Tab 3 Diagnosis or prognostic markers of HCC with extracellular vesicles as carrier

3 循环肿瘤细胞中的标志物

循环肿瘤细胞指从实体肿瘤病灶(原发灶、转移灶)脱落进入外周血的各类肿瘤细胞。肿瘤DNA可从原发性或转移性肿瘤及进入癌症患者血液中的循环肿瘤细胞中释放出来[65]。使用CanPatrol富集技术和原位杂交进行循环肿瘤细胞检测,发现90.18%的HCC患者中可检出一定水平的循环肿瘤细胞[66],且其含量与HCC的TNM分期密切相关[67],有望用于HCC的预后判断[68-69]

目前普遍认为,大多数循环肿瘤DNA(circulating tumor DNA,ctDNA)来自凋亡和坏死的肿瘤细胞,这些细胞释放片段化的DNA到循环中,理论上,ctDNA含有与其来源的肿瘤细胞相同的遗传缺陷[70-73]。目前ctDNA的检测分析方法主要分为两大类:(1)针对少量突变位点检测,如鉴定非小细胞肺癌患者中的表皮生长因子受体突变;(2)采用高通量测序手段对多基因区域的ctDNA进行检测,但检出的基因组突变可能为体细胞突变。

HCC患者的血浆中还存在大量来自其他细胞的循环游离DNA(circulating cell-free DNA, cfDNA),这些小片段DNA主要由细胞凋亡产生[74-75]。有研究发现cfDNA水平(临界值73.0 ng/mL)具有区分HCC和丙型肝炎病毒感染的潜在作用,灵敏度为69.2%,特异度为93.3%[76]。大量研究证明,cfDNA与AFP联用可以提高HCC的诊断灵敏度[77-78]。但是,目前研究中所运用的cfDNA的提取、分离、富集、检测方法各不相同,对于cfDNA水平升高的定义没有统一的标准,因此cfDNA血浆水平在HCC早期筛查中的作用还有待商榷。

除了血浆cfDNA水平的异常升高外,HCC患者中还可以检测到cfDNA的单核苷酸突变、拷贝数畸变、异常甲基化等。cfDNA的异常变化可能具有HCC筛查和诊断的临床应用价值,但往往不能单独作为HCC的诊断标准[79]。近年来,对于血浆中cfDNA的异常甲基化的相关研究已经有了更为深入的进展。Wong等[80]应用甲基化特异性PCR技术发现,在HCC患者的血浆、血清、组织样本中检测异常甲基化p15、p16,并发现p15/p16甲基化与HCC进展有关。此后,许多研究人员分析了HCC患者的cfDNA甲基化谱。在90%的HCC患者中检测到Ras关联域家族1A(Ras association domain family protein 1 isoform A,RASSF1A)启动子高甲基化[81],据此可以将HCC患者与健康对照和慢性丙型肝炎患者区分开,准确度分别为77.5%和72.5%。启动子区域的高甲基化极有可能是肿瘤发生的重要早期事件。因此,cfDNA中的启动子异常甲基化往往意味着HCC发生的高风险。另外有研究通过检测2 554例样本(1 204例HCC,392例慢性乙肝/肝硬化,958例正常对照)血浆cfDNA中5-羟甲基胞嘧啶(5-hydroxymethylcytosine,5-hmc)的表达情况,从中发现一组血浆cfDNA上的5-hmc标签能准确的判断早期肝癌的发生,AUC为0.855(95% CI 0.818~0.893)[82]。循环肿瘤细胞中的肝癌诊断或进展标志物见表 4

表 4 循环肿瘤细胞中的HCC诊断或进展标志物 Tab 4 Markers of HCC diagnosis or progression in circulating tumor cells

循环肿瘤细胞、ctDNA是目前液体活检技术中的热门方向,具有微创、可重复、可动态监测等优点,有助于患者进行HCC早筛、制定个体化治疗方案以及监测是否复发。依目前的检测技术来看,循环肿瘤细胞、ctDNA作为HCC的诊断标准存在很多限制,如ctDNA在早期HCC患者中含量较少,且容易受到cfDNA的干扰。

4 展望

由于检测的便捷性、经济性及易重复等优点,血清中直接可检出的标志物是目前应用最为广泛的HCC诊断标志物,其中最为常用的为AFP,应用于HCC的早筛。AFP-L3和DCP也已经在临床中应用,而GP73等蛋白类标志物、血清N-糖组及血清糖蛋白糖链及多分子联合诊断模型对HCC的诊断效能仍需进一步的验证。单个标志物的诊断效能往往受到多方面因素的限制,灵敏度和特异度有限,且较多关于诊断标志物的研究使用的队列样本有限,还有待多中心、大样本的队列验证。因此,研究人员尝试将多个生物标志物联合应用以提高HCC诊断的效能,但是这些多分子诊断模型目前仍仅限于研究层面,在临床上尚未有更好的分子标志物可以取代AFP用于大规模的筛查。核酸类标志物miRNA、lncRNA和circRNA是当前血清中可直接检出生物标志物研究的新方向,多项研究表明其水平与HCC的进展密切相关,然而该类标志物检测的稳定性及其预测HCC的效能也还有待进一步验证。

细胞外囊泡作为核酸、蛋白等生物活性分子的运输载体,在细胞之间的信息传递中起着重要作用。既往研究表明细胞外囊泡中运输的内容物具有一定程度的富集,水平差异较组织本底水平可能更为显著,且具有一定的稳定性,因此,细胞外囊泡中的成分有望成为新型的非侵入性辅助诊断肝癌的生物标志物。但是在细胞外囊泡分子生物标志物进入临床应用阶段前仍有需要解决的技术瓶颈,例如目前细胞外囊泡的抽提最为广泛使用的方法仍为高速离心法,耗时较长,且对分离操作有一定的技术要求;其纯化及鉴定也需要标准化的操作规范和质量控制,成本较血清中可直接检出的标志物显然更高。同时,细胞外囊泡的释放及其对生物活性物质的特异性选择机制均尚未阐明,不同处理条件是否会造成抽提和检测偏差还有待进一步深入研究。

循环肿瘤细胞、ctDNA是液体活检技术中的热门方向,具有微创、可重复、可动态监测等优点,有助于患者进行HCC早筛、制定个体化治疗方案及监测是否复发。依目前的检测技术来看,循环肿瘤细胞、ctDNA作为HCC的诊断标准存在很多限制,例如,ctDNA仅占总cfDNA的一小部分,还存在被大量非肿瘤来源的DNA稀释的风险;该方法相比之下成本更高,耗时更长,且稳定性更低,因此基于ctDNA的检测尚未大量开展。然而,随着液体活检技术的进步,循环肿瘤细胞、ctDNA的检测或可在肿瘤起始的早期阶段比血清学中的标志物更早预警肿瘤的发生,有助于将HCC的早期筛查时间更向前推进一步。

随着生物信息学技术的进步,我们已经迎来了大数据时代,肿瘤的精准分子分型和人工智能技术水平的不断提高,将为疾病的诊断方法提供更多的模型和新的思路,未来多种方法、多个标志物的联合使用或许能为肝癌的早诊早筛和预后判断提供更为准确的参考。

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