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头颈部肿瘤转移

时间:2023-04-24 理论教育 版权反馈
【摘要】:此类肿瘤多数与吸烟有关,并且肿瘤部位常取决于患者烟龄。某部位肿瘤的局部转移发生率与该部位的淋巴网密度有密切关系。肿瘤的原发部位是决定淋巴结转移发生率的主要因素之一。咽喉部、舌背和口底病变的淋巴结转移发生率较高。唾液腺肿瘤的淋巴结转移发生率一般较低,但在很大程度上受恶性肿瘤组织类型的影响。与其他部位肿瘤相比,头颈部肿瘤发生远处转移的概率相对较低。

◎Sarbani Ghosh-Laskar,Jai Prakash Agarwal,Indranial Mallick,Ketayuun Dinshaw

头颈部肿瘤是指一组起源于头颈部不同组织的多种不同肿瘤。世界各地的头颈癌发生率不相同,累积年龄标准化发生率男性为18.4,女性为8.7[1]。此类肿瘤多数与吸烟有关,并且肿瘤部位常取决于患者烟龄。它主要是一种局限性病变,且局部治疗失败较全身病变更常见。该区域的某些恶性肿瘤更易发生远处转移,如未分化的鼻咽癌和囊状泪腺癌。尽管局部病变的诊断和治疗已取得了一定进展,但一旦发生了全身转移,则没有有效的治疗方法。尚不能预测哪些患者会复发或者发生远处转移。

7.5.1 转移的发生率和部位

(1) 头颈部肿瘤的淋巴结转移

从颅底到上纵隔分布着丰富的淋巴结网,使得头颈部原发癌更容易发生局部淋巴结转移。肿瘤细胞浸润突破固有层后就会侵袭淋巴系统毛细管,即发生淋巴结转移。淋巴管道之间有着丰富的交通连接,并通常与颈部对侧淋巴管相通。某部位肿瘤的局部转移发生率与该部位的淋巴网密度有密切关系。淋巴丰富的部位(如鼻咽部和喉咽部)发生淋巴结转移的概率远远高于淋巴很少或者没有淋巴分布的部位(如鼻旁窦、声门、中耳和眼眶)。

1948年,Rouviere首次详细地描述了头颈部淋巴系统[2]。即便如此,直至20世纪90年代淋巴结组的系统命名仍然变化多样,且混乱不清。1992年,TNM(恶性肿瘤的TNM分期系统)采用将头颈部淋巴结分成12组的命名系统[3]。由美国耳鼻喉咽-头颈外科学会支持下建立的Robbins分类系统,因为更适用于颈部淋巴清扫而被接受为标准命名系统[4]。Robbins分类将头颈部淋巴结分为7个区,均有明确的解剖界限,可作为标准颈部淋巴清扫操作的标志(图7-6)。此种分类法快速地被采用,并普遍用于描述头颈癌的淋巴结转移。

(2) 淋巴结转移的发生率和分布

临床上淋巴结转移的发生率和分布在头颈的外科手术和放疗方案制订方面发挥很大作用。表7-6汇集了在这一解剖区域淋巴结转移的发生率,这些数据来自多家最大的公立医院,包括作者自己所在的孟买塔塔纪念医院[5-13]

肿瘤的原发部位是决定淋巴结转移发生率的主要因素之一。咽喉部、舌背和口底病变的淋巴结转移发生率较高。如肿瘤位于喉头、鼻旁窦或者耳部,则淋巴结转移发生率较低。唾液腺肿瘤的淋巴结转移发生率一般较低,但在很大程度上受恶性肿瘤组织类型的影响。

图7-6 颈部淋巴结分布(Robbins分类系统)

表7-6 不同部位头颈部肿瘤临床淋巴结转移的发生率

(资料来源: Bataini[5],Candela[6,7],Lindberg[8],Northrop[9], Shah[10],Laskar[11],Rao[12],以及Terhaard[13])

临床和放射学诊断颈部淋巴结阴性的患者相当一部分在颈部淋巴结清扫时可发现隐匿性淋巴结转移。一些大宗回顾性研究报道发生隐匿性转移的比例高达33%[6,7,10,14]。基于一发表的数据,Mendenhall等制订了一个根据T分级的头颈部不同解剖部位发生隐匿性淋巴结转移可能性的风险分组系统。位于口底、硬腭、口腔黏膜、磨牙后三角区和牙龈的T1肿瘤发生淋巴结转移的概率低于20%,并且在某些选择性病例无需检查颈部[15]就能看到。

临床和隐匿性淋巴结转移的分布主要取决于原位瘤的部位(表7-6)[5,6,8,9,16-19]。位于口腔前部和口咽部的原发瘤主要引流至Ⅰ~Ⅲ区,而下部喉咽和喉头的肿瘤更容易转移到Ⅱ~Ⅳ区。而鼻咽部癌,尽管位于颅骨中央部位,却易发生后方和下方颈部淋巴结转移,发生率接近30%[20]。那些病理阳性的淋巴结分布一般与有临床表现的淋巴结转移分布相一致。发生临床转移的患者在接受颈部清扫后,常常在有明显转移淋巴结的下站发现隐匿性淋巴转移,这就要求在进行外科或者放疗时要包括至少下一站的淋巴结[10]

由颅底扩展到第3颈椎边缘的咽后淋巴结是很特殊的一组。它们既不属于Robbins分区的一部分(因为它们很少被清扫到),在临床上也很少被发现。结合全身放射学检查结果的研究显示咽后淋巴结转移在鼻咽原发肿瘤的发生率最高(达70% ~90%),其次为咽壁(20%)和软腭(10%~15%),其他部位原发瘤仅有5%的可能性,甚至更少[21-23]

对侧淋巴结受累的总体概率较低,但位于中轴部位的肿瘤(如咽、喉和口腔底部的肿瘤)或者那些具有交叉淋巴管的肿瘤发生对侧淋巴结转移的概率较高(表7-7)。对侧受累的淋巴结一般与同侧淋巴结位于相同水平。

尽管淋巴结转移大多为一系列整齐有秩序的渐进发展,但也有确切的证据表明头颈部的许多肿瘤,尤其是口腔癌,可能发生跳跃式转移。发生此种转移概率为2% ~15%,舌癌的发生率最高,可发生Ⅲ~Ⅳ区的淋巴结转移,而不发生Ⅰ~Ⅱ区转移[24,25]

(3) 头颈部肿瘤的远处转移

与其他部位肿瘤相比,头颈部肿瘤发生远处转移的概率相对较低。目前临床上很少见。大多数报道的初诊时远处转移发生率低于2%[26,27]。在一项关于区域进展性疾病的研究中发现发生远处转移的概率为12%[28]

在接受根治性治疗长期随访患者的大宗回顾性研究中,鳞状细胞癌发生远处转移的检出率为 4.2% ~15.1%[26,27,29-32],见表7-8。大部分病例远处转移发生较早, 80%的于诊断后两年内发生[31]。经尸体解剖发现的转移率更高,较未尸检的报道高达40%[33,34]。这些数据反映了更晚期疾病谱,同时也说明了在尸检时多数患者患有持续性或者复发性疾病。

根据发生率,远处转移的最常见部位是肺、骨、肝、皮肤和远处淋巴结。已报道的其他被报道的不常见转移部位可发生在脑、肾上腺、肾、心、脾和膀胱[35-42]

表7-7 淋巴结转移的分布

注: CL/BL:对侧或双侧淋巴结; N0:在颈部淋巴结阴性病例中的发生率;N+:在颈部淋巴结阳性病例中的发生率(资料来源: Bataini[5], Candela[6],Lindberg[8],Northrop[9],Byers[16],Shah[17],Woolgar[18],Buckley[19])。

表7-8 有关临床远处转移发生率的部分大宗回顾性研究报道

远处转移常见于肺部。肺部丰富的毛细血管床是循环中肿瘤细胞最可能的种植地点。肺可以单独受累,有55%~85%的患者同时也合并有其他部位的转移。大约50%的患者只发生肺部远处转移[30]

发生远处转移的患者中有19%~32%的患者伴有骨转移。未分化鼻咽癌发生骨转移的概率要高于分化的鳞状细胞癌[31]。大部分骨转移发生在全身骨骼的中轴系统,其中75%的骨转移患者转移到脊椎、骨盆和颅骨[32]。有研究用18-氟脱氧18FDG-PET方法检查出头颈部肿瘤在骨盆和股骨的多发隐匿性转移灶[43]

肝脏是头颈部肿瘤的第三常见转移部位,发生率为6%~24%。尽管肝脏不是发生远处转移的首要部位,也不是唯一受累的器官,但也是口咽癌和未分化鼻咽癌的常见受累器官[31]

有5%~10%的远处转移患者会发生皮肤或者皮下组织转移。鳞状细胞癌(SCC)的发生率较低(1% ~2%),而某些罕见的非典型类癌的发病率则相对较高[44-46]。皮肤的淋巴管在皮肤和皮下组织转移中发挥了重要作用,由于肿瘤浸润或外科治疗引起的淋巴管阻塞常导致反常的淋巴流动和转移细胞的停滞[47]。此种直接的淋巴浸润模式比血行转移常见。

非局部淋巴结转移常见于腋前淋巴结和纵隔淋巴结。一个大宗回顾性综述发现锁骨下淋巴结转移发生率为1.5%,而远处淋巴结的总转移率为8%[48]。通过尸体解剖发现腋前淋巴结转移率为2%~9%[49,50],高于皮肤转移的概率[51]。腋窝淋巴结转移可能由颈静脉和锁骨下静脉交界处的淋巴液逆行流动引起的,这通常是肿瘤生长或者手术、放疗的结果。纵隔淋巴结转移并不常见,但颈部下端的肿瘤,如喉咽部和颈段食管部的肿瘤,发生隐匿性转移的概率相当高[52,53]

头颈部鳞状细胞癌发生脑转移的并不常见,仅占发生转移患者的2%~6%[31,33,54,55]。一般而言,单个转移灶较多发转移常见。单纯的脑转移是非常罕见的,有明确的证据表明超过90%脑转移的患者同时伴随着其他部位的转移[56]。脑转移常见于未分化鼻咽癌和腺样囊腺癌[39,57,58]

由于某些特定组织类型的肿瘤更容易发生远处转移,所以更值得关注。腺样囊腺癌发生远处转移的概率通常高于30%[59-61]。口腔原发癌的转移概率则相对较低[62]

肺仍然是最常见的转移器官。神经源性播散也是脑转移发生率相对较高的原因。远处转移通常意味着晚期病变,一旦发生了远处转移,其中位生存期为2~3年[60,61]

7.5.2 转移性肿瘤的临床表现

颈部淋巴结转移最初表现为颈部无痛性可移动的肿块,它们不断增大并向包膜外扩展,使得肿块与周围的神经血管束和肌肉粘连固定。神经一旦受到癌细胞侵袭就会出现疼痛和麻痹。皮肤浸润可能会引起外在伤口。少见的情况是血管壁浸润和破坏引起出血。

远处转移部位是决定其临床表现的主要因素。患者通常无临床症状,仅仅在常规体检中发现转移灶。这种情况在如腺样囊腺癌等组织类型的患者更常见。转移性肿瘤的临床表现常与治疗后的后遗症相混淆,因此保持高度怀疑的态度是及时诊断的关键,不过这对于最终结局可能并无实质性意义。

肺部转移的症状包括咳嗽、胸痛、呼吸急促和咯血。诊断的困难是区别单发转移还是第二处原发瘤,尤其是在没有局部复发证据的情况下。骨痛或者脊柱压缩性骨折并伴随神经功能缺失或破坏见于骨转移。恶性高钙血症及其相关的症状是发生广泛骨转移比较罕见的临床表现。颅内压升高、癫痫和脑卒中提示发生脑转移或者是发生了颅内病灶或颅底转移性肿瘤。

患者的临床表现决定了评估转移性肿瘤的调查方向。同样需要清楚原位病变的情况。但是,没有有力的资料说明早期发现全身转移性肿瘤及积极治疗能够改变疾病的最终结局。

7.5.3 转移的预测

准确地预测转移潜能非常重要。基于其恶性潜能进行肿瘤风险分级是非常有用的,不仅有利于建立研究模式,还有助于确定最合适的治疗方案,以保证最佳疗效的同时也节约了不必要的耗费并降低并发症发生率。许多临床、病理学和生物学因素已经证明可用于预测转移性肿瘤。尽管许多方法已用于临床,但仍有很多方法需要更多的研究和实验。

(1) 临床和组织病理学预测转移的指标

很多临床和组织病理学参数与肿瘤转移的危险分级相关。既往吸烟病史是一项重要病因学指标。已知吸烟相关原发肿瘤的生物学行为不同于非吸烟相关癌症,前者原发肿瘤表现为更具侵袭表型[63,64]。人乳头状瘤病毒(HPV)很可能是相当一部分没有吸烟史患者的病因学因素。HPV相关肿瘤更容易发生广泛淋巴结转移。但,这些肿瘤对于标准放疗和化疗等非手术治疗方法更敏感,并且预后一般较好,发生远处转移的概率也较低[65-67]

如前所述,原发肿瘤的部位是决定淋巴结转移的关键因素。不同部位的原发肿瘤淋巴结转移发生率差异很大(表7-8),并且明显影响选择治疗方案。

原发肿瘤的大小及浸润到周围软组织和骨骼等是决定T分期的因素。肿瘤分期高与淋巴结和远处转移率高相关[8,10,14]。骨侵袭同时也预示了淋巴结转移的可能[68,69]

原发肿瘤的组织类型是决定转移潜能的另一个关键因素。从组织学上看,未分化的鼻咽癌和腺样囊性癌就是一类远处转移率非常高的肿瘤。在鳞状细胞癌中,如果基底细胞变异活跃,癌细胞就更容易向远处转移[70,71]

原发肿瘤的分级也是其生物学行为的一个标志。有研究表明,低分化鳞状细胞癌和分级较高的唾液腺癌发生转移的概率都较高[61,72-73]

原发肿瘤切除后,肿瘤组织病理学上特有的特征是淋巴结和远处转移的关键因素。淋巴管的癌栓和神经周围的肿瘤浸润均与远处转移和淋巴结浸润有关系[74-76]。口腔癌中,肿瘤细胞浸润深度是极其重要的方面。舌癌中,肿瘤细胞的浸润深度达到5mm及以上的患者发生淋巴结转移的概率是表浅癌的两倍[77-80]。在一项关于舌癌患者的前瞻性随机研究中发现,肿瘤细胞浸润深度是否达4mm,是进行颈淋巴结清扫的有用临床鉴别指标[81]

淋巴结转移的许多特征有助于预测是否伴有局部和远处转移。两个甚至更多的转移结节、左右两侧的淋巴结、包膜外浸润的出现以及发现下一站淋巴结转移(Ⅳ、Ⅴ、Ⅶ级)都有助于判断是否转移的指标[30,31,44,45,48,73,82-86]

(2) 生物学预测转移的指标

传统的肿瘤分期方法主要包括肿瘤和淋巴结转移的解剖学和物理学特征。然而,对肿瘤内在生物学行为的更全面了解可能有助于更好地预测肿瘤的自然发展。因为原发肿瘤可能含有一些可能预测肿瘤转移潜能的分子生物学特征,目前已有研究致力于检测可用于临床预测的生物学标记。

表7-9概括了肿瘤转移相关的生物学标记,包括基因和它们的蛋白产物,这些可能参与肿瘤转移过程中的每一阶段,包括增殖、与周围细胞失联、通过间质迁移、侵袭血管和淋巴管及归巢到淋巴结或远处器官等。这些步骤包含多个可能同时发生的细胞特性改变,进而引起基因及其产物的改变。因此,要想准确地预测肿瘤转移潜能,不仅要识别肿瘤自身的单个标记,还要了解其在整个生物环境中的组合和相互作用。

至今未发现任何一个单个生物学标记与淋巴结或远处转移有确切的关联,即使是那些与转移关系非常大的生物学标记也不能简单地纳入肿瘤样本的标准评估中。多个标记联合的预测价值可能大于单个标记。比较基因杂交(CGH)和组织微阵列技术可用于评估组合标记。这两项技术均是在早期阶段作为检测工具用于检测肿瘤转移相关的生物学标记[113-115]。这些高通量技术具有通过同时分型大量标记进一步提高目前生物学标记在头颈部肿瘤中的预测价值。

表7-9 预测转移的生物学标记

在将这些标记融入作为评估头颈部肿瘤转移的主流之前仍有许多障碍需要克服。首先,需要利用多种不同的方法评估各项参数,这些参数具有多样化的敏感性和标准。因此,标准统一并规范化是一项困难的工作。其次,一小块活检组织标本的生物学特性并不能完全代表整个肿瘤组织的真实状况,影响肿瘤整个生物学行为的恶性细胞克隆可能并不存在于这块小的活检标本内。然而,随着对基因翻译研究兴趣的不断增加,以及对头颈部肿瘤生物学的更深入认识,两者促进了致力于研究预测转移癌生物标记的更规范实验。许多关于这方面的研究已有了许多非常优秀的综述[116-118]

7.5.4 转移性肿瘤的诊断性检测

在过去的几十年里为了检查是否发生了转移,进行了大量的研究,从开始单纯的临床分析,演变为后来的临床评估与生物学成像和生物学分析相结合。

评估颈部淋巴结转移的标准成像技术包括CT、磁共振成像(MRI)和超声(US)。超声引导下的穿刺活检细胞学技术(US-FNAC)也得到了应用。CT和MRI检测淋巴结转移的总敏感性超过80%。然而,它们的特异性差异较大,为40%~80%[119-121]。超声的敏感性和特异性分别为70%~96%和75%~95%[120,122]。FNAC和US两者联合可得到较高的特异性,据报道可高达95%~100%[119,122,123]

一项荟萃分析比较了这些评价淋巴结转移的标准策略,发现US和US-FNAC的诊断优势高于CT和MRI[124]。而CT和MRI更常被用作常规检查使用,它们的最大优势是能够同时对原发病变进行分期。为了得到最理想的结果, US和US-FANC技术需要额外的培训和经验。这两项技术不同检查医生之间的检查结果误差较大,并且不适用于检查位置较深及周围有骨质空腔的淋巴结(如咽后淋巴结)。遗憾的是,对于经颈部淋巴清扫术确认存在的隐匿性转移淋巴结,常规成像技术的检出率不足50%[125,126]

CT和MRI在淋巴结转移检出方面的表现基本相似。有一项研究报道了对于小淋巴结的检测,MRI可能更有优势。已有报道说使用一种含有超微小氧化物离子(USPIO)的增强剂并通过其功能性特征区别良性和恶性淋巴肿大。这项技术的敏感性和特异性分别为84% ~87%和77% ~97%。利用这项技术可能会减少对肿大淋巴结节假阳性的诊断[127-129]。由于转移病灶的检出率非常低,所以转移癌的检查在传统上也仅限于头颈部。多数情况下,可用的检查方法仅有胸部X线检查。发生远处转移较常见的部位可以通过骨扫描、腹部B超或者CT扫描检查来排除骨转移和肝转移。然而,由于特异性差及较高的花费,在没有临床症状的情况下是很少做这些检查的。

最近,生物学成像已经对诊断性肿瘤成像产生很大影响。基于生物学而不是形态学特征鉴别肿瘤和正常组织的能力更为突出。已有许多研究评价正电子发射断层扫描(PET)和PET-CT技术在诊断头颈部肿瘤是否发生淋巴结和远处转移中的价值。18F-FDG是最常用的同位素。许多研究比较PET和标准放射技术在头颈部肿瘤中的应用,并得到了不同结果[126,130-132]。已有一项荟萃分析评估18F-FDG-PET技术用于检查颈部转移病灶的价值[133]。PET的敏感性和特异性分别为79%(95% CI)和86%(95% CI)。相对的,CT、MRI或US-FANC等标准影像学诊断技术的敏感性和特异性分别为75%和79%。尽管前者有所提高,但并没有统计学意义。PET对于隐匿性转移灶的检出率仅有50% (95%CI),但这个结果相对于传统影像学技术的45%并没有显著的提高,尽管其特异性保持较高为87%。FDG-PET在空间分辨率的局限性及其靠近相对活跃的唾液腺,这都可能是导致其不能达到最优效果的原因。这些研究都说明一点,尽管FDG-PET淋巴结分期方面较常规影像学诊断技术有一定优势,但这些优势还不足以使FDG-PET作为头颈癌的常规检查项目。阴性颈部淋巴结手术清扫以识别并清除微播散仍是最佳的治疗方案。

将生物显像检查作为发现远处转移的常规检查手段不可能经济实惠。然而,对于那些远处转移发生率较高的病例选择性地使用18F-FDG-PET等策略则可能有一定好处。其中PET最常被用于评估鼻咽癌患者,因为其发生颈部下段和远处转移的概率相对较高。许多研究报道了PET在颈部分期中应用的进步,但其在肿瘤最初分期的作用则仍不清楚[20,134,135]。一项关于FDG-PET的研究显示其对头颈部癌隐匿性骨转移有较高的检出率[43]。在这项研究中,在许多没有转移的临床和生化证据的患者在早期发现骨转移。因此,那些发生远处转移的高危患者应考虑进行PET扫描检查,这也可能会改变治疗方案。

尽管PET作为头颈部肿瘤最初的常规诊断评估方法并未带来显著好处,但它在描述原发病变和转移部位特征方面确实有较突出的优势。这些结果可能会影响到治疗过程,如颈部清扫范围和放射靶区体积。有几项研究报道,依据PET划定放疗治疗计划[136-138]。PET还被用于肿瘤缺氧的无创性检查。18F-MISO(misonidazole,甲氧甲基硝基咪唑乙醇,一种选择性地聚集在缺氧组织的硝基咪唑)已被用于检查包括头颈部在内的许多部位。其他还有顺式氟代硝基咪唑(fluoroerythronitroimidazole,F-FETNIM)和氟代硝基咪唑-阿拉伯氟糖(fluoroazomycin-arabinofuranoside,F-FAZA)也在研发过程中,它们不仅可帮助判断预后,还可有助于生物学指导放疗治疗方案的制订(参见“新兴治疗备选方案”章节)。

目前还没有任何生化检测方法被推荐作为淋巴结或远处转移的诊断常规。肝功能检查对肝脏转移有一定的价值,但是对于较小或者早期病灶的敏感性则非常低,生物标记的使用仍处于研究阶段(参见“预测性检查”章节)。更常用的是多个分子预后标记,病毒性病原学标记的使用也越来越多,包括p16免疫组化染色、原位杂交以及反转录RCR (RT-PCR)检测HPV感染,由于其具有预后价值而常用于口咽癌;应用实时定量PCR检测循环EB病毒(EBV)DNA滴度以及地方鼻咽癌患者病变组织中EBV编码的早期RNAs (EBER1和EBER2)。已有研究表明循环EBV-DNA水平可用于预测远处转移和生存率[112]。表皮生长因子受体(EGFR)过表达或扩增可通过包括免疫组化法(IHC)和原位杂交荧光法(FISH)等多种技术检测。其他还包括免疫组化检测缺氧诱导因子HIFla、CAIX、赖氨酸氧化酶,以及用ELISA检测血浆骨桥蛋白水平。比较基因组杂交技术和组织微阵列技术已被用于检测多基因和基因表达产物,这些可将头颈部肿瘤分为不同风险谱,并可能采用不同的治疗方案。

7.5.5 转移性肿瘤的预后判断

出现淋巴结或远处转移对头颈性肿瘤患者的预后有非常大的影响。在占大多数的局限性病变中,淋巴结转移灶的出现是影响生存率的主要因素。图7-7描述了淋巴结分期对患者总生存率、无病生存和淋巴结控制的影响,这些均是来自Tata纪念医院1999~2000年未发表的研究数据。已有大量研究报道了淋巴结分期对患者疾病的独立预后作用[139-141],而笔者有关头颈部肿瘤的经验也与此相同[142,143]

图7-7 淋巴结分期对头颈部肿瘤预后的影响

注: 资料来自Tata纪念医院肿瘤放射科1990~2000年1805例头颈部肿瘤患者(包括所有位置及分期)的无瘤生存率(DFS)和淋巴结控制(NC)情况的分析。

区域性淋巴结转移的多项指标具有预后价值,其中淋巴结的数目和大小最重要,直接影响头颈部肿瘤的分期。淋巴结的大小和活动度决定了其可切除性、淋巴结复发的机会及包膜外扩散(ECE)的概率。病理学检查显示淋巴结大小超过3cm,发生包膜外扩散的概率高于80%[144-146]。淋巴结大小不仅是局部病变控制的重要影响因素,同样也是发生远处转移的重要风险因素[44,145,147-149]。受累淋巴结的数量也是评估发生远处转移概率和长期存活的重要因素[44,149-150]

淋巴结转移的部位意义显著。有一项研究发现随着颈部更低水平淋巴结出现转移,其患者总体生存进行性变差,Ⅰb水平淋巴结转移患者生存率为37%,而V水平者为21%[151]。也有许多研究提示淋巴结转移与预测癌症局部控制有一定的关联性,尽管这一点尚未被明确证实[152]。淋巴结复发的风险与这些预测因素有关,并且关系到最初治疗的详细计划,包括治疗策略的选择以及手术和放疗水平等[153-155]。Tata纪念医院里那些接受选择性颈部淋巴结清扫的患者淋巴结复发中有30%发生在廓清范围以外[155]。有许多研究发现,常规显微镜检查难以发现淋巴结微转移灶的免疫组化特征证据,被认为与局部复发有关[156]。同样,较长的无瘤生存期(DFI)预示预后良好及补救性治疗对肿瘤的长期控制[157,158]

出现远处转移无疑提示预后差,1年生存率为20% ~40%[29,159]。一些研究报道许多因素可能影响发生远处转移患者的生存率[159-162]。仅有一处转移的患者预后好于多处转移患者。肝转移和肺转移提示预后更差。DFI也可预测那些发生远处转移并接受了治疗患者的生存率。

7.5.6 转移性肿瘤的治疗

(1) 标准治疗方法

1) 淋巴结转移的治疗原则

头颈部肿瘤的颈部淋巴结转移治疗大多与原位癌治疗同时进行,手术和放疗(联合或不联合化疗或生物治疗)治疗淋巴结转移同样有效,因此,通常根据原发肿瘤的最合适治疗方法来选择淋巴结转移的治疗方案。如果转移负荷非常小或无临床症状,单一的治疗方法通常是足够的。对于那些更进展期者,选择多种治疗方法(通常3种方法全选)联合使用最合适。因为淋巴结大小正常的隐匿性转移的临床或现有影像学诊断手段的敏感性很低,所以即便在临床和影像学诊断均阴性的情况下仍常需要选择性颈部治疗。

手术治疗包括颈部淋巴清扫。颈部广泛清扫术包括整个颈部纵轴上所有淋巴结的切除。经典的根治性颈部清扫术是切除浅表和深部颈筋膜及其所有淋巴结(Ⅰ~V区),同时切除胸锁乳突肌、肩胛舌骨肌、颈内颈外静脉的颈部脊髓副神经及颌下腺。改良颈部清扫术保留了某些组织,这种手术方式不仅减少了死亡率,同时改善组织功能,并未影响疾病控制。选择性颈部清扫术的切除范围更小,包括有选择切除部分淋巴结,如肩胛上(Ⅰ~Ⅲ区)、外侧面(Ⅱ~Ⅴ区)及后外侧(Ⅱ~Ⅴ区)清扫。选择性清扫术多用于颈部临床阴性的病例及在放疗后残留淋巴结的补救性治疗。改良颈部清扫术仍是标准术式。

放疗也可用作颈部肿瘤的一种选择和治疗方案。头颈部肿瘤的传统放疗通常使用4~6MV线性加速器或远距离钴-60照射装置。短距离放疗通常不用于此类淋巴结转移。

放疗的剂量与分割依赖于治疗指证。临床放射学阳性的区域选择60~72Gy,每天使用标准的分级1.8~2Gy。选择性治疗区域使用最小剂量50Gy,也有相同分割体积。还有使用其他不同剂量与分割的放疗方案。超分割或加速放疗对于局部病变的控制和提高生存率的确实有一定的优势,尽管优势较小。超分割放疗通常用于减轻局部病变或远处转移灶。

放疗的范围取决于淋巴结分级、原发瘤的位置和临床症状及组织学类型。从简单的双侧或前外侧方向到更复杂的三维适形放射(3DCRT)和调强放疗(IMRT)技术,均可将最大剂量的放射线集中到肿瘤,最大限度地保护包括脊髓、唾液腺、吞咽肌和喉头结构等正常组织。

放疗和化疗的联合应用已经提高了临床疗效。研究证明,对高危患者(风险主要决定于淋巴结的状态)接受根治性和辅助性放疗时,联合应用以铂类为基础的化疗,可以明显改善局限性病灶的疗效和总体存活率[163,164]

2) 颈部淋巴结阴性的治疗

颈部选择性治疗是基于亚临床转移的估计发生率。颈部清扫术或放疗可有效控制90%的亚临床转移,治疗方案的选择主要依据原发肿瘤的最佳治疗方案[165]。当手术为治疗原发疾病的主要手段时,如隐匿性淋巴结转移发生率超过10%~15%,则强烈推荐进行淋巴结清扫。如果预期转移发生率较低,密切随访足够。对于需要手术的患者,最常选择改良淋巴结清扫。早期口腔癌采用选择性淋巴清扫多已足够,特别是联合冷冻切片评估怀疑转移淋巴结,并作好预案,一旦发现转移淋巴结阳性则应扩大清扫范围。

放疗策略通常包括治疗窗内有转移风险的不同水平淋巴结。通常,为实现这个目标会增加一点花费和并发症等代价。双侧颈部选择性照射包括对侧几个隐匿性转移风险高的亚区域。

颈部保守治疗后孤立淋巴结复发率为20%~30%,补救性治疗成功率为70%~80%[165]

3) 颈部淋巴结阳性的治疗

对于选择性淋巴结治疗,淋巴结转移阳性最初治疗方案的选择主要依据原发灶的最适当选择方案。当首选手术时,对没有包膜外扩展(ECE)单个同侧淋巴结转移者只做改良淋巴结清扫是足够的[166,167];对大的或者多发的淋巴结以及ECE者需辅以放化疗以降低局部复发率[164,168]

如首选非手术治疗,对淋巴结阳性的头颈部鳞状细胞癌目前标准的治疗方案是放疗联合化疗或生物学疗法(使用西妥昔单抗)[163]。4~8周的放疗或者放化疗联合治疗后已完全控制缩小的单个较小淋巴结转移,不再需要其他治疗。根据病灶的大小和形态学特征,影像学上怀疑仍有残留病灶者,需要实施淋巴结清扫。一些研究推荐对N2b~N3患者接受放疗产生临床放射学完全反应后,应例行选择性淋巴结清扫[169-171],而另一些研究则建议采取更加保守的随访(“wait and watch”)策略[172]。我们的策略是对于影像学检查有明确ECE证据的体积较大的淋巴结转移,在放疗后应进行选择性颈部淋巴结清扫。敏感的影像学方法例如US-FNAC、PET扫描,可帮助我们挑选淋巴结复发率高的高危患者[173-176]

淋巴结转移的控制依赖于淋巴结的初始分期和主要治疗策略。如果只使用单一疗法,肿瘤局部复发率从N1的10%~15%增加到N3的40%~60%。联合手术和放疗,通常可使进展期淋巴结转移患者的淋巴结复发率减少一半[177]。大多数淋巴结转移病情控制失败与局部治疗失败有关。孤立的颈部复发较少见,发病率小于10%[178,179]。孤立性颈部复发的补救性治疗通常基于原先的治疗方案。有25%~60%孤立性肿瘤复发选择补救性手术治疗,其中1/3的患者可得到长期控制[180,181]。补救治疗方案的选择依赖于淋巴结的大小、固定性和先前的治疗措施。放疗同样扮演重要角色,可以联合手术或者单独用于治疗[157]

4) 远处转移癌的治疗

头颈部癌的转移很少是患者的最初主诉。远处转移癌者的预后一般较差,因为其对全身治疗的反应相对较差。发生远处转移后,尽管接受治疗,但患者的中位生存时间为6~9个月。因此,需非常审慎地选择全身治疗和局部治疗,包括放疗和手术治疗以及专业的支持治疗。多数病例治疗的目的仅是缓解症状。当远处转移发生后,以下因素决定治疗的范围和程度:病人的状态、是否有明显合并症、局部病灶情况、DFI以及所应用的主要治疗手段。

标准的系统治疗由化疗药物组成,通常是以铂类为基础的抗肿瘤药物,如联合5-FU或者紫杉醇,可较单一用药提高反应率。但是,Ⅲ期临床研究发现这种联合用药没有显著提高生存率[182,183]。反应率很少超过30%,表明上皮性恶性肿瘤对标准系统治疗的耐药。因此,如果采用全身系统疗法需要权衡利弊。靶向治疗是转移疾病系统治疗中的研究焦点。在复发或转移性头颈部肿瘤的Ⅲ期随机试验中,联合应用西妥昔单抗,比单独使用铂类化疗药物可以小幅度提高生存率[184]。许多其他靶向治疗药物尚处在研发的不同阶段。

许多情况下也可采用局部治疗,如肺部单一或少量的转移灶,可采用局部切除术[158,185]。在选择性病例中,完全切除率高达80%~90%,5年生存率为30%~50%。因此,如能控制局部病变,这种疗法可明显改善生存。其他部位的转移癌,局部治疗的目的主要是减轻症状。骨转移通常需要姑息放疗,通常使用低剂量分割放疗,从单剂量8Gy到两周30Gy。对脑转移患者通常予以剂量20~30Gy姑息性全脑放疗。单一的脑转移尽管比较少见,但可联合使用全脑放疗和手术切除或立体定向RT加速器[186-189]。淋巴结转移,尤其是腋窝淋巴结转移,如果没有其他部位转移,可以考虑淋巴结切除。

(2) 头颈部肿瘤转移的治疗新策略

在过去几十年里,头颈部肿瘤的标准治疗方案已经演变为包括多种方法的综合治疗策略,这确实使患者预后有一定改善,所以需要更先进的治疗手段。但对进展期肿瘤和转移性肿瘤的无瘤生存和总体生存期,以及早期肿瘤的标准治疗相关并发症发生率等方面均需进一步改进。

现阶段系统治疗策略研究主要集中于靶向治疗。靶向治疗是指特异性作用于携带有特定靶分子细胞的一类治疗,而对其他细胞的功能无明显影响。总的来说,常用的靶向治疗包括两种形式——单克隆抗体(m Abs)和小分子酪氨酸激酶抑制因子(TKIs)。头颈部肿瘤中最有前途的靶分子包括表皮生长因子受体家族(erb B)、Src通路及血管生成通路。临床不同阶段的靶向治疗见表7-10。

表7-10 头颈部肿瘤的靶向治疗药物

续表

注: COX:环氧化酶;EGFR:表皮生长因子受体;PDGF:血小板衍生生长因子;m Ab:单克隆抗体;TKI:酪氨酸激酶抑制剂;VEGF:血管内皮生长因子;VEGFR:VEGF受体(资料来自: Clinical Trials.gov,2008年9月20日更新)。

表皮生长因子受体属酪氨酸激酶家族的erb B成员,参与多种生长调控通路。这个家族有4个成员:EGFR、Her-2/neu、Her-3和Her-4。前面两个在HNSCC中发挥了重要作用。90%的HNSCC有EGFR的过表达,它的高表达往往预示淋巴结转移和预后不良[190,191]。Her-2/neu的过表达较少见,见于17%~53%的HNSCC,它在HNSCC中的角色很可能是EGFR的信号配体,它的表达同样和一系列疾病的较差转归有关[192,193]。在抗EGFR治疗中,西妥昔单抗不仅可明显提高复发肿瘤患者的生存率(西妥昔单抗联合放疗对比单纯放疗)[194],同时也可提高转移癌患者的生存率(与铂类化疗药联合)[184]。这两种治疗方法均被FDA批准。目前已有超过100个临床试验研究如西妥昔单抗和新型TKIs、厄洛替尼、吉非替尼和拉帕替尼等药物的治疗效果。

Src激酶是另外一组与酪氨酸激酶受体(包括EGFR)、血小板衍生生长因子(PDGFR)、胰岛素样生长因子-1受体(IGF-1R)和G蛋白耦联受体(GPCRs)信号通路联系紧密的激酶。这个家族中,c-Src的过度表达见于多种肿瘤,包括头颈部肿瘤[195]。这些激酶表达的异常提示肿瘤进展或转移[196]。在HNSCC中,Scr激酶与EGFR的激活和抑制相关联[197]。针对Scr的靶向药物是新近发展的药物,许多TKIs,尤其是达沙替尼,正被用于与标准治疗联合使用治疗复发性和转移癌的研究中。

血管生成在肿瘤发展中发挥了非常重要的作用,它受血管生成促进因子和抑制因子的调控。血管内皮生长因子(VEGF)家族是最重要的血管生成促进因子,VEGF配体和它们的受体(VEGFR1,2,3)是抗血管生成生物治疗的理想目标。可抑制VEGF 配体的单克隆抗体贝伐单抗以及VEGF受体的多个TKIs,如索拉菲尼、索坦和凡德他尼正在进行临床试验。

在过去几十年里,放疗策略已经改变,强调适形递送放射剂量到形状复杂的照射靶区,保护正常组织结构,从而能够对受累区域(原发灶和淋巴结)的增强剂量照射。精确的图像引导技术可提供精确定位,使得肿瘤放疗专家能进一步减少不确定边界范围。生物成像技术为划定肿瘤轮廓提供了新的手段,如在多个中心PET已用于肿瘤轮廓的划定。初步的感觉是它可能导致预期放射体积的改变。

下一步就是使用生物成像技术描绘肿瘤不同部分的特征,并可以根据其特征对其使用不同剂量的放射线,即“数字剂量分布”(theragnostics或dose painting by numbers)概念[198]。肿瘤和淋巴结内的缺氧区域显然是放疗的首要目标。PET成像技术可将同位素(F-MISO、F-FAZA、Cu-ATSM)聚集于缺氧区域,已与CT放射技术联合应用,用于确定靶区内的缺氧部位,以指导使用不同的剂量和分割大小治疗[199-203]。联合使用全身化疗和生物药物如西妥昔单抗,可进一步增强放疗对局部进展病变的治疗效果。硝基咪唑类药物尼莫唑作为缺氧细胞的增敏剂,已经成功地与放疗联合应用[204]。如果肿瘤组织具有缺氧特征,这些则可以作为辅助放疗的有价值药物。

现在外科研究中一种新的方法就是对颈部N0早期病变患者进行前哨淋巴结活检,帮助制订最终的手术方案。许多研究,主要有关口腔肿瘤,已经检验这种方法的可行性和诊断准确性[205-208]。淋巴闪烁造影术,应用放射胶体和术中γ照相机,对于前哨淋巴结的检出率可达90%。多数情况下,这种方法的阴性预测率也可达90%。但在更晚期肿瘤其检测结果则不恒定。在早期无淋巴结转移的HNSCC患者,这种方法可能会成为一种可接受的常规检查方法。

7.5.7 将来研究的方向

与20世纪比,尽管肿瘤治疗方法已有一定进展,但人们也认识到虽然有了大量技术和经费的投入,但肿瘤患者生存率的提高却停滞不前,改善的步伐缓慢。这使人们认识到肿瘤的诊断和治疗不能单纯依赖以大小和数量为基础的物理方法。标准分期和治疗常常是基于经验性的,并过分依赖这些物理学参数。进一步提高疗效必须了解肿瘤的分子机制,这才能理解为何肿瘤组织看上去相似但却有不一样的行为表现。这个过程是渐进性的长期过程。不过现在已找到了新的研究途径,如果继续发展,很可能会带来突破。

头颈部转移肿瘤的研究重点已渐渐转移到肿瘤的生物学上。进一步转化研究,将使这些研究更接近临床。必须更好地认识分子标记及其功能,更加明确是单独应用还是与其他标记联合应用。这不仅能预测疾病预后,还能根据其生物学特征进行肿瘤分组,并预测发生转移的概率。分子学诊断技术(如微阵列)可帮助我们以多种特征为基础,将每一种肿瘤进行分类。放射学技术应该可根据其生物学特征预测发生转移的风险性,同时也可以评判对放疗和化疗的敏感性。治疗应该基于物理学和生物学特征,从而对低危病变进行低剂量治疗,对高危病变给予更加积极的治疗。相同的肿瘤和转移病灶也可以根据其内部特征给予不同剂量的放疗。全身治疗也可根据个体化原则,针对每例肿瘤生物学特征进行治疗。多模式治疗方案将在联合、顺序等方面进一步优化,以达到肿瘤治疗的最佳目标,即最大限度地杀死肿瘤组织,并将并发症发生率降到最低。

(梁磊 译,钦伦秀 审校)

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