SMARCA4/BRG1缺陷型非小细胞肺癌的临床病理特点和治疗策略

SWI/SNF复合体是一个含有10~15个亚基的多蛋白复合体,参与重要的细胞进程和功能调控,突变频率较高,最常见的突变亚基为SMARCA4/BRG1。SMARCA4/BRG1缺失的非小细胞肺癌(SMARCA4-deficient non-small lung cancer,SMARCA4-dNSCLC)具有恶性程度高、肿瘤发展迅速、生存率低等特点。SMARCA4-dNSCLC经常发生SMARCA4和KRAS、TP53、KEAP1、STK11共突变的情况,但ALK、EGFR、ROS1等常见突变几乎均为阴性,因此传统的肺癌治疗模式对SMARCA4-dNSCLC效果有限,新型治疗策略的出现或是解决问题的关键。本文将对SMARCA4-dNSCLC的临床病理特点和新型治疗策略进行综述。     

SWI/SNF染色质重塑复合体及其与肿瘤病理生理相关性的研究进展

SWI/SNF复合体是具有ATP酶活性的染色质结构重塑复合体,通过调控核小体空间位置、结构的方式产生相应表观遗传学效应。SWI/SNF复合体表观遗传学效应主要涉及细胞增殖、分化及DNA修复等过程,其有序进行密切相关复合体的完整性。体细胞内,累及SWI/SNF复合体编码基因的失能性突变可造成其亚基缺失,并破坏相关细胞生理活动的有序进行。最终,导致多种肿瘤的发生与进展。全基因组测序示,SWI/SNF复合体编码基因失能性突变比例在泛癌组织中达25%,略低于经典抑癌基因TP53编码基因突变率(26%)。SWI/SNF复合体内亚基缺失所产生的促癌效应具有多层次性。在表观遗传学层面,亚基缺失可阻遏SWI/SNF复合体有效拮抗多种癌症相关表观遗传学效应因子,如PRC合体的转录效应。导致细胞去分化或过度增殖。在基因组层面,由于SWI/SNF复合体参与以同源重组修复为主的DNA修复进程,可导致基因组不稳定及癌症相关突变的累积。此外,亚基缺失可转变SWI/SNF复合体功能表观遗传学功能,致使其以“残余”效应促进肿瘤进展。由于SWI/SNF复合体部分亚基在细胞生理功能上存在互补性且密切参与DNA双链修复途径,靶向其特定亚基或使用PARP抑制剂,可产生合成致死效应而有效抑制SWI/SNF复合体缺陷肿瘤进展。部分SWI/SNF复合体缺陷肿瘤,如ARID1A缺陷型,其肿瘤免疫微环境存在显著抑制状态,使其对肿瘤免疫治疗存在良好的敏感性。     

胃SMARCA4缺失性未分化癌6例临床病理分析

目的 探讨胃SMARCA4缺失性未分化癌(SMARCA4DUC)的临床病理特征、免疫表型、鉴别诊断及预后。方法 收集6例确诊为胃SMARCA4DUC患者的临床病理资料,总结其组织学特点及免疫表型,并复习相关文献。结果 6例患者中男5例、女1例,中位年龄65(49～72)岁。镜下表现为肿瘤细胞呈弥漫片状分布,细胞黏附性差,局部区域可呈横纹肌样,细胞质丰富、嗜酸,核呈空泡状,核仁明显,核分裂相易见,肿瘤内常见大片状坏死。免疫组化显示：6例肿瘤细胞SMARCA4均完全缺失表达(6/6),而SMARCB1均阳性表达(4/4);上皮标志物AE1/AE3部分患者阳性(4/6),其中1例为弥漫阳性,3例为点灶弱阳性;神经内分泌标志物SYN大部分患者局部中等程度阳性(5/6);Ki-67增殖指数约70%～80%。5例患者获得随访,3例1 a内死亡。结论 胃SMARCA4DUC是一类少见的高度恶性肿瘤,预后差。由于肿瘤缺乏特异性分化,易被误诊,熟悉这一肿瘤的特点并行SMARCA4、SMARCB1检测有助于诊断。     

STK11基因突变与非小细胞肺癌免疫治疗相关性研究进展

肺癌是最常见的恶性肿瘤之一。在全球范围内,肺癌的发病率及死亡率都极高且呈上升趋势。近年来,免疫检查点抑制剂（ICIs）在晚期非小细胞型肺癌治疗中产生了显著的生存优势,然而对于驱动基因阳性的非小细胞肺癌患者,免疫检查点抑制剂疗效不佳。但一些抑癌基因可以通过突变或缺失等方式对免疫治疗产生不同程度的影响,其中丝氨酸/苏氨酸激酶11（STK11）基因突变与PD-1/PD-L1免疫检查点抑制剂有效性密切相关,研究发现STK11突变与免疫细胞浸润减少、PD-L1低表达和对PD-L1抑制反应差有关。本文就非小细胞肺癌中STK11基因突变与免疫治疗相关性的研究进展作一综述。     

EGFR/TP53/RB1三重突变的小细胞肺癌转化研究及治疗进展

表皮生长因子受体（epidermal growth factor receptor,EGFR）突变型非小细胞肺癌（non-small cell lung cancer,NSCLC）患者在接受EGFR酪氨酸激酶抑制剂（tyrosine kinase inhibitors, TKIs ）靶向治疗后能获得临床获益,但之后会不可避免地出现获得性耐药,而发生小细胞肺癌（small cell lung cancer,SCLC）组织学转化被认为是一种罕见的耐药机制。随着二代基因检测（next- generation sequencing,NGS）技术的快速发展及广泛应用,研究者发现存在EGFR/TP53/RB1三重突变的NSCLC经靶向治疗后更容易发生SCLC组织学转化,并且转化型SCLC疗效及预后较差。本文对近年来关于EGFR突变的NSCLC发生SCLC组织学转化的研究作一综述,涉及相关的转化机制、可能有效的新型药物及治疗策略,为EGFR/TP53/RB1三重突变的转化型SCLC患者提供更多潜在的临床治疗选择。      

MEK抑制剂在EGFR-TKI靶向治疗非小细胞肺癌中的作用

非小细胞肺癌是最常见的肺癌,最常见的基因突变是EGFR突变,EGFR-TKI已被用于治疗含这类突变的患者。然而,随着治疗进展,患者逐渐出现耐药性导致治疗失败。主要原因是EGFR信号通路下游重新激活,其中RAS/RAF/MEK/ERK和PI3K/AKT/PKC途径最重要。ERK1/2信号再激活可产生对EGFR抑制剂的抗性。目前临床研究已经发现,MEK抑制剂可以抑制ERK磷酸化,从而阻止随后的MAP激酶下游磷酸化,并因此诱导肿瘤活动的退化和停滞。大量试验表明,ERK途径的持续激活有助于获得吉非替尼耐药性。MEK抑制剂还可以诱导细胞周期阻滞和凋亡。本文总结了MEK抑制剂和EGFR-TKI的作用及其在NSCLC治疗中的作用,为肺癌分子靶向治疗提供了新思路。     

PD-1/PD-L1免疫抑制剂在非小细胞肺癌免疫治疗中的研究进展

摘 要：近年来免疫检查点领域研究进展迅速,众多新药相继出现,其中包括程序性细胞死亡蛋白1（programmed cell death protein 1,PD-1）单抗Pembrolizumab和Nivolumab,程序性细胞死亡蛋白配体1（programmed cell death protein ligand 1,PD-L1）单抗Atezolizumab。免疫检查点PD-1/PD-L1抑制剂给EGFR突变阳性非小细胞肺癌患者带来更多的生存获益,正逐渐改变国内外EGFR突变阳性晚期非小细胞肺癌的治疗模式。全文对PD-1/PD-L1为靶向的肿瘤免疫治疗在晚期EGFR突变阳性非小细胞肺癌患者治疗中的研究进展进行综述。     

罕见EGFR L833V/H835L复合突变的肺腺癌患者1例及文献回顾

表皮生长因子受体(epidermal growth factor receptor,EGFR)突变是非小细胞肺癌(non-small cell lung cancer,NSCLC)发生发展过程中最常见的驱动基因,其中18-21号外显子的突变常见,尤其是19号外显子的缺失和21号外显子L858R点突变最为常见,但是EGFR L833V/H835L罕见基因复合突变的发生率非常低,患者数量很少,相关临床数据和治疗方法的证据也不足。部分EGFR-酪氨酸激酶抑制剂(EGFR-tyrosine kinase inhibitors,EGFR-TKIs)在治疗伴有罕见基因突变的肺癌患者方面同样具有良好疗效。本文报道了1例携带EGFR L833V/H835L罕见基因复合突变的NSCLC患者,在给予阿法替尼治疗5个月后,计算机断层扫描(computed tomography,CT)显示肺部病灶缩小,患者对阿法替尼联合安罗替尼治疗反应良好。同时,我们还对以往报道的EGFR L833V/H835L罕见基因复合突变的NSCLC患者进行了整理,总结了该类患者的特点及应用不同种类EGFR-TKIs治疗的效果。     

EGFR突变晚期非小细胞肺癌免疫治疗的研究进展

肺癌是全球癌症相关死亡的主要原因。表皮生长因子受体是亚洲肺腺癌患者最常见的突变类型。酪氨酸激酶抑制剂是表皮生长因子受体突变非小细胞肺癌一线首选治疗，但获得性耐药限制了其长期疗效，对于耐药后治疗仍没有有效选择方案。目前，免疫治疗延长了部分患者的生存时间,但在表皮生长因子受体突变非小细胞肺癌中反应较差，介导其疗效不佳的原因仍尚不明确。多种生物标志物的联合评价更能准确预测其免疫治疗疗效并筛选潜在获益人群。联合抗血管生成及新型靶点药物治疗具有免疫增敏作用。本文就表皮生长因子受体突变晚期非小细胞肺癌免疫治疗研究现状、免疫治疗潜在获益人群及免疫联合治疗新策略进行综述。     

表皮生长因子受体基因20号外显子插入突变型非小细胞肺癌的治疗现状与展望

自表皮生长因子受体(EGFR)基因突变被发现以来,酪氨酸激酶抑制剂(TKI)的应用拉开了EGFR阳性非小细胞肺癌精准靶向治疗的序幕。携带EGFR基因常见的两类经典代表性突变,即第19号外显子框内缺失突变和第21号外显子L858R点突变(约占所有EGFR突变的90%)的非小细胞肺癌患者,接受TKI靶向治疗的临床获益远远优于传统化疗。EGFR基因第20号外显子插入突变却与众不同,在剩余10%EGFR少见基因突变中为最常见的类型,且这类突变中的绝大多数对目前临床应用的第一、二、三代TKI原发耐药,临床预后差。目前,国际上亦缺乏针对此突变的深入研究和临床治疗指南。文章介绍了EGFR基因20号外显子插入突变型非小细胞肺癌的发病机制、氨基酸序列亚型和治疗现状,探讨了此突变在目前肺癌治疗领域所面临的挑战与展望。     

Clinicopathologic Characteristics of BRG1-Deficient NSCLC

IntroductionTen percent of NSCLCs harbor mutations in SMARCA4, the gene encoding the SWItch/Sucrose Non-Fermentable ATPase BRG1. In preclinical models, BRG1 inactivation increases tumor aggressiveness but enhances sensitivity to drugs that target oxidative phosphorylation and inhibit SMARCA2, EZH2, CDK4, or CDK6. To facilitate translation of preclinical findings into clinical studies exploiting these therapeutic vulnerabilities, we assessed the clinical features of patients with tumors harboring BRG1-inactivating mutations.MethodsData sets from Massachusetts General Hospital and Foundation Medicine were reviewed to determine the prevalence of SMARCA4-mutant NSCLC and describe its clinicopathologic characteristics. BRG1 expression was evaluated by immunohistochemistry and correlated with SMARCA4 mutations. Treatment outcomes were retrospectively assessed.ResultsWe detected SMARCA4 genomic alterations in 9% (n = 117 of 1422) and 11% (n = 3188 of 27,281) of NSCLCs in the institutional and Foundation Medicine data sets, respectively. In both cohorts, truncating mutations comprised over one-third of SMARCA4 alterations. Twenty-nine of 64 SMARCA4-mutant NSCLCs (45%) assessed for BRG1 expression reported loss of expression, most (90%) of which had truncating SMARCA4 mutations. Overall, 84% (n = 26 of 31) of evaluated NSCLCs with truncating SMARCA4 mutations lacked BRG1 expression. Deficient BRG1 expression was predominantly detected in adenocarcinomas with co-occurring mutations in KRAS, TP53, KEAP1, and STK11. Among patients with BRG1-deficient NSCLC who received first-line platinum doublet chemotherapy (n = 11) or chemotherapy plus immunotherapy (n = 5), median progression-free survival was 38 days and 35 days, respectively.ConclusionsBRG1 deficiency is enriched in NSCLCs with truncating SMARCA4 mutations. Clinical outcomes are poor in this molecular subgroup, highlighting the importance of developing novel strategies to target unique vulnerabilities associated with the BRG1-deficient state.     

SWI/SNF complexes are required for full activation of the DNA-damage response

SWI/SNF complexes utilize BRG1 (also known as SMARCA4) or BRM (also known as SMARCA2) as alternative catalytic subunits with ATPase activity to remodel chromatin. These chromatin-remodeling complexes are required for mammalian development and are mutated in ~20% of all human primary tumors. Yet our knowledge of their tumor-suppressor mechanism is limited. To investigate the role of SWI/SNF complexes in the DNA-damage response (DDR), we used shRNAs to deplete BRG1 and BRM and then exposed these cells to a panel of 6 genotoxic agents. Compared to controls, the shRNA knockdown cells were hypersensitive to certain genotoxic agents that cause double-strand breaks (DSBs) associated with stalled/collapsed replication forks but not to ionizing radiation-induced DSBs that arise independently of DNA replication. These findings were supported by our analysis of DDR kinases, which demonstrated a more prominent role for SWI/SNF in the activation of the ATR-Chk1 pathway than the ATM-Chk2 pathway. Surprisingly, γH2AX induction was attenuated in shRNA knockdown cells exposed to a topoisomerase II inhibitor (etoposide) but not to other genotoxic agents including IR. However, this finding is compatible with recent studies linking SWI/SNF with TOP2A and TOP2BP1. Depletion of BRG1 and BRM did not result in genomic instability in a tumor-derived cell line but did result in nucleoplasmic bridges in normal human fibroblasts. Taken together, these results suggest that SWI/SNF tumor-suppressor activity involves a role in the DDR to attenuate replicative stress and genomic instability. These results may also help to inform the selection of chemotherapeutics for tumors deficient for SWI/SNF function.     

SMARCA4-Deficient Thoracic Sarcomatoid Tumors Represent Primarily Smoking-Related Undifferentiated Carcinomas Rather Than Primary Thoracic Sarcomas

IntroductionHighly aggressive thoracic neoplasms characterized by SMARCA4 (BRG1) deficiency and undifferentiated round cell or rhabdoid morphology have been recently described and proposed to represent thoracic sarcomas. However, it remains unclear whether such tumors may instead represent sarcomatoid carcinomas, and how their clinicopathologic characteristics compare with those of nonsarcomatoid SMARCA4-deficient non–small cell lung carcinomas (SD-NSCC).MethodsWe identified 22 SMARCA4-deficient thoracic sarcomatoid tumors (SD-TSTs) with round cell and/or rhabdoid morphology and 45 SD-NSCCs, and comprehensively analyzed their clinicopathologic, immunohistochemical, and genomic characteristics using 341–468 gene next-generation sequencing and other molecular platforms.ResultsThe relationship of SD-TSTs with NSCC was supported by (1) the presence of NSCC components juxtaposed with sarcomatoid areas in five cases, (2) focal expression of NSCC lineage markers TTF1 or p40 in four additional cases, (3) smoking history in all except one patient (mean = 51 pack-years), accompanied by genomic smoking signature, and (4) high tumor mutation burden (mean = 14.2 mutations per megabase) and mutations characteristic of NSCC in a subset. Compared with SD-NSCCs, SD-TSTs exhibited considerably larger primary tumor size (p < 0.0001), worse survival (p = 0.004), and more frequent presentation at younger age (30–50 years) despite heavier smoking history. Distinctive pathologic features of SD-TSTs included consistent lack of adhesion molecule claudin-4, SMARCA2 (BRM) codeficiency, and frequent expression of stem cell markers.ConclusionsSD-TSTs represent primarily smoking-associated undifferentiated/de-differentiated carcinomas rather than primary thoracic sarcomas. Despite their histogenetic relationship with NSCC, these tumors have unique clinicopathologic characteristics, supporting their recognition as a distinct entity. Further studies are warranted to determine therapeutic approaches to this novel class of exceptionally aggressive thoracic tumors.     

Solid‐type poorly differentiated adenocarcinoma of the stomach: Deficiency of mismatch repair and SWI/SNF complex

ARID1A, one of the subunits in SWI/SNF chromatin remodeling complex, is frequently mutated in gastric cancers with microsatellite instability (MSI). The most frequent MSI in solid‐type poorly differentiated adenocarcinoma (PDA) has been reported, but the SWI/SNF complex status in solid‐type PDA is still largely unknown. We retrospectively analyzed 54 cases of solid‐type PDA for the expressions of mismatch repair (MMR) proteins (MLH1, PMS2, MSH2, and MSH6), SWI/SNF complex subunits (ARID1A, INI1, BRG1, BRM, BAF155, and BAF170) and EBER, and mutations in KRAS and BRAF. We analyzed 40 cases of another histological type of gastric cancer as a control group. The solid‐type PDAs showed coexisting glandular components (76%), MMR deficiency (39%), and complete/partial loss of ARID1A (31%/7%), INI1 (4%/4%), BRG1 (48%/30%), BRM (33%/33%), BAF155 (13%/41%), and BAF170 (6%/2%), EBER positivity (4%), KRAS mutation (2%), and BRAF mutation (2%). Compared to the control group, MMR deficiency and losses of ARID1A, BRG1, BRM, and BAF155 were significantly frequent in solid‐type PDAs. Mismatch repair deficiency was associated with the losses of ARID1A, BRG1, and BAF155 in solid‐type PDAs. In the MMR‐deficient group, solid components showed significantly more frequent losses of ARID1A, BRG1, BRM, and BAF155 compared to glandular components (P = .0268, P = .0181, P = .0224, and P = .0071, respectively). In the MMR‐proficient group, solid components showed significantly more frequent loss of BRG1 compared to glandular components (P = .012). In conclusion, solid‐type PDAs showed frequent losses of MMR proteins and the SWI/SNF complex. We suggest that loss of the SWI/SNF complex could induce a morphological shift from differentiated‐type adenocarcinoma to solid‐type PDA.     

The reversible epigenetic silencing of BRM: implications for clinical targeted therapy

The SWI/SNF chromatin-remodeling complex serves as a master switch that directs and limits the execution of specific cellular programs, such as differentiation and growth control. SWI/SNF function requires one of two paralogous ATPase subunits, Brahma (BRM) or BRM-related gene 1 (BRG1), which we previously found are lost together in cancer cell lines and primary lung cancers. Although BRG1 has been found to be mutated in cancer cell lines, the mechanisms underlying BRM silencing are not known. To address this question, we sequenced BRM in 10 BRM/BRG1-deficient cancer cell lines and found that BRM was devoid of abrogating mutations. Moreover, histone deacetylase (HDAC) inhibitors restored BRM expression in each of these BRG1/BRM-deficient cancer cell lines, indicating that epigenetic silencing is a major mechanism underlying the loss of BRM expression. Despite their ability to restore BRM expression, these HDAC inhibitors also blocked BRM function when present. However, after their removal, we observed that BRM expression remained elevated for several days, and during this period, BRM activity was detected. We also found that the suppression of BRM occurs in a broad range of human tumor types and that loss of one or both BRM alleles potentiated tumor development in mice. Thus, BRG1 and BRM are silenced by different mechanisms, and it may be possible to clinically target and reexpress BRM in a number of tumor types, potentially impacting tumor development.