最近由英國(guó)倫敦癌癥研究所的Marco Gerlinger博士發(fā)表的一項(xiàng)嚴(yán)謹(jǐn)?shù)幕蚪M學(xué)研究,，進(jìn)一步強(qiáng)調(diào)可以將癌癥視為癌細(xì)胞的異質(zhì)性集合,，這些癌細(xì)胞不斷進(jìn)化，甚至可能以達(dá)爾文的方式為爭(zhēng)取生存權(quán)和發(fā)展權(quán)而發(fā)生競(jìng)爭(zhēng),，而代價(jià)是宿主的健康乃至生命,。相關(guān)論文由近期的New England Journal of Medicine發(fā)表。
當(dāng)上世紀(jì)90年代,，主流觀點(diǎn)認(rèn)為癌癥的起因是單個(gè)細(xì)胞的突變(常由煙草或射線暴露所致),，隨著時(shí)間推移，這個(gè)細(xì)胞分裂數(shù)百次而發(fā)展成一個(gè)具有相同惡性的細(xì)胞“克隆群”,，能夠阻止人體免疫和癌癥監(jiān)視系統(tǒng),，最終形成腫瘤。如果任其發(fā)展,，這一單克隆腫瘤會(huì)逐漸擴(kuò)散到全身,，達(dá)到手術(shù)無(wú)法治愈的程度，使細(xì)胞毒化療成為唯一的選擇,。
這種腫瘤進(jìn)化的概念主要是圍繞腫瘤的生長(zhǎng),，以及可增加腫瘤侵襲性的額外突變的獲得。腫瘤進(jìn)展的多步模型暗示我們,，癌癥本質(zhì)上是一種單克隆的壞東西,，可通過(guò)及時(shí)的外科治療加以清除,，或采用化療將其擊退。但這種便于醫(yī)學(xué)生理解的過(guò)于簡(jiǎn)單化的模型,，近年來(lái)已受到質(zhì)疑,，因?yàn)獒槍?duì)腫瘤組織的遺傳學(xué)研究顯示，腫瘤比我們?cè)日J(rèn)為的更有活力和更具有異質(zhì)性,。
Gerlinger博士及其同事檢測(cè)了4例進(jìn)展期腎癌患者的原發(fā)灶和轉(zhuǎn)移灶標(biāo)本,。在多個(gè)時(shí)間點(diǎn)進(jìn)行基因組分析，包括化療開(kāi)始之前和癌癥進(jìn)展過(guò)程中,?；蚪M分析包括全外顯子組測(cè)序，或所有已知人類基因的DNA測(cè)序（參見(jiàn)“Personalized Genome Around the Corner?”）,，試圖在原發(fā)灶轉(zhuǎn)移時(shí)和化療后的新遺傳突變中尋找腫瘤進(jìn)化的跡象,。此外，研究者還得以觀察同一時(shí)間點(diǎn),、同一標(biāo)本的不同區(qū)域,，直接尋找舊有概念中的惡性單克隆組織。
研究結(jié)果表明,，存在基于不同時(shí)間點(diǎn)和化療暴露與否的腫瘤異質(zhì)性,。在1例患者的十多份標(biāo)本中(其中9份來(lái)自手術(shù)切除原發(fā)灶的不同區(qū)域)，分析確認(rèn)了125種基因突變,。隨后在一個(gè)亞組的標(biāo)本中驗(yàn)證最初的基因組分析結(jié)果,。
研究者得到了一些有趣的發(fā)現(xiàn)：所有活檢標(biāo)本的突變中，大約1/3符合單克隆模型,；另有45%的突變?yōu)椴糠帜[瘤標(biāo)本所共有，僅有略多于20%的突變僅存在于單次活檢標(biāo)本中,。這意味著,，總的來(lái)說(shuō)，檢測(cè)出的突變多數(shù)并非所有腫瘤標(biāo)本所共有,，區(qū)域差異在腫瘤中相當(dāng)普遍,。
雖然并非所有突變都可能參與癌癥的行為，但這些數(shù)據(jù)表明一個(gè)腫瘤在遺傳方面是不均勻的,，特定的腫瘤區(qū)域具有獨(dú)特的遺傳特性,。或許有些突變僅存在于若干個(gè)甚至單個(gè)細(xì)胞中,，盡管本項(xiàng)研究未能達(dá)到如此高的采樣細(xì)致度,。
有趣的是，某些突變似乎出現(xiàn)1次以上,，隨著腫瘤進(jìn)展,，這些突變?cè)谀[瘤中暫時(shí)增加,，而這正是一種“趨同進(jìn)化”(編者注：是指不同的生物，如果生活在條件相同的環(huán)境中,，有可能產(chǎn)生功能相同或極相似的形態(tài)結(jié)構(gòu),，以適應(yīng)相同的條件)的表現(xiàn)。這提示我們,，多樣的自然選擇壓力——或許包括化療暴露——使得腫瘤在達(dá)爾文式選擇過(guò)程中發(fā)生有利于自身生長(zhǎng)和繁殖的適應(yīng)性改變,。
腫瘤內(nèi)部存在異質(zhì)性和“達(dá)爾文式致癌”的事實(shí)，需要我們嚴(yán)肅對(duì)待,。這意味著不僅每例患者的每個(gè)腫瘤都具有獨(dú)特的基質(zhì),，而且還是多個(gè)獨(dú)特的癌細(xì)胞群體的集合。
就像DNA指紋顯示每個(gè)人（除了同卵雙胞胎）都具有獨(dú)特的基因那樣,，這些腫瘤數(shù)據(jù)表明,，每個(gè)癌癥也是獨(dú)一無(wú)二的，甚至同一個(gè)人的同一個(gè)癌癥也在不斷進(jìn)化,。這種變異可能解釋為何化療并不是總能根治腫瘤,。此外，這些數(shù)據(jù)還帶來(lái)了一個(gè)問(wèn)題,，即如何針對(duì)具有異質(zhì)性且不斷進(jìn)化的處于活動(dòng)狀態(tài)的腫瘤制定個(gè)性化的治療方案,。
正如研究者所說(shuō)的，只有量化和理解這種變化,，才能更好地了解癌癥預(yù)后和發(fā)展新的治療策略,。(生物谷Bioon.com)
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PMID: 22397650
Intratumor Heterogeneity and Branched Evolution Revealed by Multiregion Sequencing
Marco Gerlinger, M.D., Andrew J. Rowan, B.Sc., Stuart Horswell, M.Math., James Larkin, M.D., Ph.D., David Endesfelder, Dip.Math., Eva Gronroos, Ph.D., Pierre Martinez, Ph.D., Nicholas Matthews, B.Sc., Aengus Stewart, M.Sc., Patrick Tarpey, Ph.D., Ignacio Varela, Ph.D., Benjamin Phillimore, B.Sc., Sharmin Begum, M.Sc., Neil Q. McDonald, Ph.D., Adam Butler, B.Sc., David Jones, M.Sc., Keiran Raine, M.Sc., Calli Latimer, B.Sc., Claudio R. Santos, Ph.D., Mahrokh Nohadani, H.N.C., Aron C. Eklund, Ph.D., Bradley Spencer-Dene, Ph.D., Graham Clark, B.Sc., Lisa Pickering, M.D., Ph.D., Gordon Stamp, M.D., Martin Gore, M.D., Ph.D., Zoltan Szallasi, M.D., Julian Downward, Ph.D., P. Andrew Futreal, Ph.D., and Charles Swanton, M.D., Ph.D.
Background
Intratumor heterogeneity may foster tumor evolution and adaptation and hinder personalized-medicine strategies that depend on results from single tumor-biopsy samples.
Methods
To examine intratumor heterogeneity, we performed exome sequencing, chromosome aberration analysis, and ploidy profiling on multiple spatially separated samples obtained from primary renal carcinomas and associated metastatic sites. We characterized the consequences of intratumor heterogeneity using immunohistochemical analysis, mutation functional analysis, and profiling of messenger RNA expression.
Results
Phylogenetic reconstruction revealed branched evolutionary tumor growth, with 63 to 69% of all somatic mutations not detectable across every tumor region. Intratumor heterogeneity was observed for a mutation within an autoinhibitory domain of the mammalian target of rapamycin (mTOR) kinase, correlating with S6 and 4EBP phosphorylation in vivo and constitutive activation of mTOR kinase activity in vitro. Mutational intratumor heterogeneity was seen for multiple tumor-suppressor genes converging on loss of function; SETD2, PTEN, and KDM5C underwent multiple distinct and spatially separated inactivating mutations within a single tumor, suggesting convergent phenotypic evolution. Gene-expression signatures of good and poor prognosis were detected in different regions of the same tumor. Allelic composition and ploidy profiling analysis revealed extensive intratumor heterogeneity, with 26 of 30 tumor samples from four tumors harboring divergent allelic-imbalance profiles and with ploidy heterogeneity in two of four tumors.
Conclusions
Intratumor heterogeneity can lead to underestimation of the tumor genomics landscape portrayed from single tumor-biopsy samples and may present major challenges to personalized-medicine and biomarker development. Intratumor heterogeneity, associated with heterogeneous protein function, may foster tumor adaptation and therapeutic failure through Darwinian selection. (Funded by the Medical Research Council and others.)
Supported by grants from the Medical Research Council, Cancer Research UK, the Royal Marsden Hospital Renal Research Fund, Novartis, EU Framework 7 Personalized RNA Interference to Enhance the Delivery of Individualized Cytotoxic and Targeted Therapeutics (PREDICT), and the Wellcome Trust (to Dr. Futreal).
This article is dedicated to Tim Christmas.
Disclosure forms provided by the authors are available with the full text of this article at NEJM.org.
Drs. Gerlinger, Larkin, Gronroos, Martinez, and Swanton and Mr. Rowan, Mr. Horswell, Mr. Endesfelder, Mr. Matthews, and Mr. Stewart contributed equally to this article.
We thank the patients; Nasir Khan, Isobelle Coombes, Kim Edmonds, Amy Thomas, Jade Griffiths, Phil Clarke, Maggie James, and Peter Campbell; and the U.K. National Institute for Health Research.
