Expression of ornithine decarboxylase in precancerous and cancerous gastric lesions

AIM: To investigate the expression of ornithine decarboxylase (ODC) in precancerous and cancerous gastric lesions. METHODS: We studied the expression of ODC in gastric mucosa from patients with chronic superficial gastritis (CSG,n = 32),chronic atrophic gastritis CAG,n = 43; 15 with and 28 without intestinal metaplasia (IM),gastric dysplasia (DYS,n = 11) and gastric cancer (GC,n = 48) tissues using immunohistochemical staining. All 134 biopsy specimens of gastric mucosa were collected by gastroscopy. METHODS: The positive rate of ODC expression was 34.4%,42.9%,73.3%,81.8% and 91.7% in cases with CSG,CAG without IM,CAG with IM,DYS and GC,respectively (P < 0.01),The positive rate of ODC expression increased in the order of CSG < CAG (without IM) < CAG (with IM) < DYS and finally,GC. In addition,ODC positive immunostaining rate was lower in well-differentiated GC than in poorly-differentiated GC (P < 0.05). CONCLUSION: The expression of ODC is positively correlated with the degree of malignity of gastric mucosa and development of gastric lesions. This finding indicates that ODC may be used as a good biomarker in the screening and diagnosis of precancerous lesions.     

Correlations among Helicobacter pylori infection and the expression of cyclooxygenase‐2 and vascular endothelial growth factor in gastric mucosa with intestinal metaplasia or dysplasia

Background and Aims: To examine the rate of Helicobacter pylori infection and the expression of cyclooxygenase‐2 (COX‐2) and vascular endothelial growth factor (VEGF) in gastric mucosa with intestinal metaplasia or dysplasia, and explore their correlations in precancerous gastric lesions. Methods: A total of 172 patients were included in the study. H. pylori infection was evaluated by hematoxylin–eosin and modified Giemsa staining. The expression of COX‐2 and VEGF proteins was detected by immunohistochemistry. Results: The rates of H. pylori infection in gastric mucosal dysplasia (DYS), intestinal metaplasia in gastric mucosa (IM), chronic atrophic gastritis (CAG) and chronic superficial gastritis (CSG) patients were significant differences (P = 0.001). The average optical density (AOD) values of COX‐2 staining in CSG, CAG, IM and DYS patients were 13.81 ± 5.53, 45.28 ± 21.44, 73.67 ± 26.02 and 91.23 ± 45.11, respectively, with significant differences among CSG, CAG and IM patients (P = 0.037, 0.001 and 0.047 for CSG vs CAG, CSG vs IM and CAG vs IM, respectively). The expression level of VEGF in DYS patients was significantly higher than those in other patients (P = 0.001, 0.001 and 0.001 for DYS vs CSG, DYS vs CAG and DYS vs IM, respectively). The expression levels of COX‐2 in H. pylori‐positive IM, CAG and DYS patients were significantly higher than those in H. pylori‐negative counterparts (P = 0.043, 0.009, 0.001, respectively). Additionally, the expression level of COX‐2 was positively correlated with that of VEGF with the aggravation of gastric mucosal lesions (r = 0.640, P = 0.006). Conclusion: H. pylori infection might be able to induce the expression of COX‐2 in precancerous gastric lesions, which in turn upregulates the expression of VEGF.     

幽门螺杆菌感染在胃癌及癌前病变中的研究

目的　研究胃癌及癌前病变与Hp感染的关系 ,以探讨Hp可能的致癌机制。 方法　经内镜和病理明确诊断的胃癌及癌前病变者共 5 48例 ,包括慢性浅表性胃炎 (CSG) 16 3例、慢性萎缩性胃炎 (CAG) 2 0 7例、肠上皮化生 (IM) 71例 ,异型增生(DYS) 4 5例及胃癌 (GC) 6 2例。每例均活检胃窦大小弯、胃角及胃体大小弯共 5块 ,以WS法检测Hp。结果　癌前病变及胃癌Hp感染均较高 ,CAG(4 2 .5 % ) ,IM(76 .1% ) ,DYS(88.9% )和GC(72 .5 % ) ,与CSG(2 3.9% )有显著性差异 (P <0 .0 5或P <0 .0 1)。随着年龄增大 ,CAG、IM、DYS和GC逐步增多 ,而且≥ 5 6岁年龄组IM、DYS和GC显著多于≤ 40岁组 (P <0 .0 5 ) ,但CSG则相反。肠型胃癌和Hp感染密切相关 (P <0 .0 5 ) ,从胃窦小弯和大弯、胃角及胃体小弯和大弯顺序 ,Hp感染随着CSG、CAG、IM、DYS和GC病变而增高 ,Hp感染部位也在上移 ,尤其在胃体小弯及大弯 ,IM、DYS和GC的Hp感染显著高于CSC部位 (P <0 0 5 )。结论　Hp感染是导致从胃炎→胃萎缩→肠化→异型增生→癌变序列发展的危险因子 ,肠型胃癌和Hp感染密切相关 ,胃镜检查应该多部位取活检作病理及Hp检测 ,尤其是高位     

胃癌中幽门螺杆菌感染与原癌基因c—met表达及预后研究

目的　研究幽门螺杆菌(Hp)感染的胃癌(GC)组织中c-met表达及(Hp)感染对胃癌预后的影响。方法　经病理证实,不同病变胃粘膜145例以免疫组化检测c-met基因表达,以W-S法及快速尿素酶试验检测(Hp)感染。结果　在浅表性胃炎(CSG)、萎缩肠化生胃炎(CAG+IM)、异型增生(DYS)、早期GC和进展期GC中,c-met基因表达率分别为25.53%,51.28%,61.54%,66.67%和68.42%,CAG+IM、DYS、GC均显著高于CSG(P＜0.05)。肠型胃癌c-met阳性表达与(Hp)感染密切相关。CAG+IM,DYS和GC组c-met阳性表达(Hp)感染者明显高于阴性组。(Hp)阳性者5年生存期显著短于(Hp)阴性者。结论　(Hp)感染和c-met表达与胃粘膜增殖和恶化有关,前者也与胃癌预后有关。     

幽门螺杆菌相关胃疾病组织中P53、iNOS的表达

目的通过检测慢性浅表性胃炎、慢性萎缩性胃炎、肠上皮化生、不典型增生、胃癌组织幽门螺杆菌（Hp）和P53、一氧化氮合成酶（iNOS），探讨Hp感染与P53、iNOS表达的关系，以及Hp感染导致胃癌的可能分子机制。方法应用快速尿素酶试验和组织切片革兰氏染色和血清HpCagA抗体检测Hp，用免疫组化SP法检测上述组织的P53、iNOS。结果慢性浅表性胃炎、慢性萎缩性胃炎、肠上皮化生、不典型增生、胃癌组织中Hp检出率分别为45．9％、68．4％、71．4％、75．O％、54．8％，病变各组中P53和iNOS表达阳性率与浅表性胃炎组比较均有显著性差异。除浅表性胃炎组、萎缩性胃炎Hp阳性组的P53表达阳性率外，各病变Hp阳性组的P53和iNOS表达阳性率与各组的Hp感染阳性率呈正相关，各病变组中Hp（＋）组的P53和iNOS表达阳性率显著高于Hp（-）组，均有显著性差异。结论Hp与P53和iNOS阳性表达有一定的相关性。     

hTERT、P53在胃癌及癌前病变中的表达及相关性研究

目的探讨端粒酶逆转录酶（hTERT）基因、p53蛋白在胃癌（GC）及癌前病变中的表达及相关性。方法采用免疫组化和原位杂交方法分别检测130例GC及癌前病变组织标本中p53和hTERT mRNA的表达。结果p53蛋白在慢性表浅性胃炎（CSG）、慢性萎缩性胃炎（CAG）、非典型增生（DYS）、GC中的表达率分别为5％、25％、50％、62．5％,其中GC与CSG、CAG比较有统计学差异：hTERT mRNA在CSG、CAG、DYS及GC中的表达率分别是0、10％、30％、78．75％,GC与CSG、CAG、DYS比较有统计学差异。p53阳性的GC组织中hTERT表达均为阳性,p53阴性的GC组织中hTERT阳性表达率为66．7％。结论hTERT是一个比p53更好的恶性肿瘤标记物;p53基因突变可导致端粒酶活化,但端粒酶激活可能不完全依赖于p53基因的调控。     

不同胃黏膜病变的细胞增殖变化规律及其意义

目的 研究胃黏膜不同病变时细胞增殖的变化规律及其意义,寻找有效的生物学指标来预测和早期诊断胃癌。方法 采用免疫组织化学SP法检测了30例慢性浅表性胃炎(CSG)、26例慢性萎缩性胃炎(CAG)、40例肠上皮化生(IM)、22例异型增生(DYS)、22例早期胃癌(EGC)和26例进展期胃癌(AGC)的增殖细胞核抗原(PCNA)、表皮生长因子受体(EGFR)、转化生长因子β受体(TGFβR)Ⅰ和TGFβR Ⅱ的表达。所得数据采用秩和检验及Spearman等级相关分析。结果 相应于CSG、CAG、IM、DYS、EGC和AGC不同的胃黏膜病变,PCNA和EGFR的表达递增(P<0.0001),TGFβR Ⅰ(P=0.007)和TGFβR Ⅱ(P<0.0001)的表达递减。PCNA标记指数在DYS时高于CSG、CAG和IM,低于EGC和AGC,其差异有显著性(P<0.0001);EGFR在IM和DYS时比CSG和CAG明显升高,差异有显著性(P<0.0001);TGFβR Ⅰ在EGC和AGC时明显下降,与CSG相比差异有显著性(P=0.007);TGFβRⅡ在AGC时明显下降,与CSG、CAG、IM、DYS及EGC相比差异有显著性(P<0.13001)。EGFR表达与PCNA的表达呈正相关,TGFβR Ⅰ和TGFβR Ⅱ与PCNA分别呈负相关,TGFβR Ⅰ和TGFβRⅡ呈正相关。结论 不同的胃黏膜病变中,DYS是细胞增殖水平发生变化的关键环节;EGFR的升高和TGFβR的下降可能通过对细胞增生水平的调节促进胃癌的发生。     

Expression of polycomb protein EZH2 in multi-stage tissues of gastric carcinogenesis

OBJECTIVE: To study the role and significance of the polycomb group (PcG) protein EZH2 (enhancer of zeste homolog 2) in the multi-step process of intestinal-type gastric carcinogenesis. METHODS: Gastric specimens were obtained from 142 patients with gastric disease, including 34 with chronic non-atrophic gastritis (NCAG), 33 chronic atrophic gastritis (CAG) with intestinal metaplasia (IM), 40 CAG with dysplasia (DYS) and 35 with intestinal-type gastric carcinomas (GC), and 32 Helicobacter pylori-negative controls. The EZH2 protein was stained by the immunohistochemical method and was expressed as the intensity and percentage of the total number of epithelial cells. The chronic gastritis and the grading of dysplasia were classified according to Chinese National Consensus on chronic gastritis and the Padova international classification. RESULTS: The EZH2 protein levels in the specimens of normal gastric tissue, NCAG, CAG with IM, DYS and intestinal-type GC were gradually increased (P < 0.05), but statistical significance was not found between the groups of DYS and GC. CONCLUSION: PcG protein EZH2 plays an important role in the multi-step process of intestinal-type gastric carcinogenesis.     

胃癌幽门螺杆菌感染中c-met基因表达与增殖的关系及其预后

目的 研究c-met基因蛋白及增殖细胞核抗原（PCNA）在幽门螺杆菌（Hp)感染的胃黏膜病变演进中的表达及关系，探讨Hp感染对胃癌预后的意义。方法 采用免疫组织化学法检测145例经病理证实不同胃黏膜病变的c-met和PCNA基因表达，Warthin-Starry法检测Hp感染。结果 在浅表性胃炎（CSG）、萎缩肠化性胃炎、异型增生（DYS）、早期胃癌和进展期胃癌中，c-met和PCNA2种基因在萎缩肠化性胃炎、DYS、胃癌均显著高于CSG（P＜0．05）。对胃黏膜增殖程度与c-met和PCNA阳性表达强度的密切关系分析，表明两者有显著关联（P＜0．01）。c-met和PCNA阳性表达与胃癌组织类型、浆膜浸润和淋巴结转移密切相关，而且Borrmann Ⅳ明显高于早期胃癌（P＜0．05）。c-met－LI和PCNA－LI在胃癌中等级相关表达有极显著的相关性（P＜0．001）。c-met阳性表达与肠型胃癌Hp感染有关。萎缩肠化性胃炎、DYS和胃癌组c-met阳性表达中Hp感染者明显高于阴性者。Hp阳性者5年生存期显著短于Hp阴性者。结论 c-met和PCNA基因表达与胃黏膜增殖和恶化有关，c-met基因可能成为评估胃癌恶化和预后的1项新的重要指标。Hp感染和c-met表达与胃黏膜增殖和恶化有关，Hp感染与胃癌预后有关。     

Hp感染与胃癌和癌前病变中p53、ras、c-myc基因表达的关系

目的研究幽门螺杆菌（Hp）感染与胃癌（GC）和癌前病变中p53、ras、c-myc基因表达的关系,以探讨其致病机制。方法用美兰和W-S特殊染色方法确定Hp感染,免疫组化SP法检测p53、ras、c-myc基因的表达。结果慢性萎缩性胃炎（CAG）、肠化生（IM）、异型增生（DYS）、GC的Hp感染率均高于慢性浅表性胃炎（CSG）（P均〈0.05）;p53、ras、c-myc基因在GC、DYS中的表达均高于CAG（P均〈0.05）,p53、ras基因在IM中的表达均高于CAG（P〈0.05）;IM中Hp阳性者的p53阳性表达率高于Hp阴性者（P〈0.05）,DYS、GC中Hp阳性者p53、ras、c-myc的表达率高于Hp阴性者（P均〈0.05）。结论Hp感染可能通过调节p53、ras、c-myc基因的表达而促进GC的发生。     

Potential therapeutic significance of increased expression of aryl hydrocarbon receptor in human gastric cancer

AIM： To determine the functional significance of aryl hydrocarbon receptor （AhR） in gastric carcinogenesis, and to explore the possible role of AhR in gastric cancer （GC） treatment. METHODS： RT-PCR, real-time PCR, and Western blotting were performed to detect AhR expression in 39 GC tissues and five GC cell lines. AhR protein was detected by immunohistochemistry （IHC） in 290 samples： 30 chronic superficial gastritis （CSG）, 30 chronic atrophic gastritis （CAG）, 30 intestinal metapiasia （IN）, 30 atypical hyperplasia （AH）, and 70 GC. The AhR agonist tetrachlorodibenzo-para-dioxin （TCDD） was used to treat AGS cells. MTr assay and flow cytometric analysis were performed to measure the viability, cell cycle and apoptosis of AGS cells.RESULTS： AhR expression was significantly increased in GC tissues and GC cell lines. IHC results indicated that the levels of AhR expression gradually increased, with the lowest levels in CSG, followed by CAG, IM, AH and GC. AhR expression and nuclear translocation were significantly higher in GC than in precancerous tissues. TCDD inhibited proliferation of AGS cells via induction of growth arrest at the G1-S phase. CONCLUSION： AhR plays an important role in gastric carcinogenesis. AhR may be a potential therapeutic target for GC treatment.     

Significance and relationship between Cripto-1 and p-STAT3 expression in gastric cancer and precancerous lesions

AIM:To explore the relationship between Cripto-1 (CR-1) and tyrosine phosphorylation STAT3 (p-STAT3) expressions in gastric cancer (GC) and gastric carcinogensis and metastasis.METHODS: The PV9000 immunohistochemical method was used to detect the expression of CR-1 and p-STAT3 in 178 cases of GC, 95 matched normal gastric mucosa, 40 chronic atrophic gastritis (CAG), 48 intestinal meta-plasia (IM) and 25 dysplasia (DYS). RESULTS: The positive rates of CR-1 and p-STAT3 expression were significantly higher in ...     

幽门螺杆菌感染和端粒酶活性以及c-myc、p16基因的表达在胃黏膜癌变中的相关性研究

幽门螺杆菌(H.pylori)是胃癌的主要致病因子,H.pylori、端粒酶和肿瘤相关基因的关系在胃黏膜癌变发生过程中研究很少。目的:观察H.pylori感染和端粒酶活性以及c-myc、p16基因在胃癌中的关系。方法:通过胃镜活检和外科手术获取171例胃组织标本,快速尿素酶试验和H.pylori培养确定有无H.pylori感染;酶联免疫法检测H.pylori感染患者的血清CagA-IgG水平;聚合酶链反应.酶联免疫吸附测定(PCR-ELISA)法检测端粒酶活性;免疫组化法检测c-myc、p16基因的表达。结果:胃癌(GC)组端粒酶表达率显著高于其他各组(P<0.01);慢性萎缩性胃炎(CAG)伴中、重度肠化(IM)组端粒酶和c-myc表达率显著高于CAG伴轻度IM组(P<0.05);而慢性浅表性胃炎(CSG)和CAG伴轻度IM组p16表达率显著高于CAG伴中、重度IM、异型增生(Dys)和GC组(P<0.05)。在CAG伴轻、中、重度IM组中,H.pylori阳性组端粒酶活性比阴性组高:无论有无H.pylori感染,胃癌组端粒酶活性都非常高。在CAG伴中、重度IM、Dys和GC组中,H.pylori阳性亚组c-myc表达显著高于阴性亚组(P<0.01),而在ECAG伴中、重度IM和Dys组中,H.pylori阳性亚组p16基因表达显著低于阴性亚组(P<0.01)。结论:H pylori感染很可能主要通过c-myc基因的激活和p16基因的失活以及其他基因的变化来诱导CAG伴中、重度     

Expression of trefoil factors 1 and 2 in precancerous condition and gastric cancer

AIM: To study the expression of trefoil factor 1 (TFF1) and TFF2 in precancerous condition and gastric cancer and to explore the relationship between TFFs and tumorigenesis, precancerous condition and gastric cancer. METHODS: The expression of TFF1 and TFF2 was immunohistochemically analyzed in paraffin-embedded samples from 140 patients including 35 cases of chronic superficial gastritis (CSG), 35 cases of gastric ulcer (GU), 35 cases of chronic atrophic gastritis (CAG) and 35 cases of gastric cancer (GC). RESULTS: TFF1 and TFF2 were located in cytoplasm of gastric mucous cells. In CSG, GU, CAG and GC, the level of TFF1 expression had a decreased tendency (P<0.05). The expression of TFF2 was higher in GU than in CSG, but the difference was not significant. The expression of TFF2 also had a decreased tendency in GU, CAG, and GC (P<0.05). CONCLUSION: The reduced expression of TFF1 and TFF2 in precancerous conditions and gastric cancer may be associated with the proliferation and malignant transformation of gastric mucosa. More investigations are needed to explore the mechanism of TFFs and the relationship between TFFs and gastric cancer.     

胃癌中幽门螺杆菌感染与胃粘膜增殖及凋亡研究

目的研究幽门螺杆菌(Hp)感染的胃癌(GC)发展中增殖细胞核抗原(PCNA)表达及细胞凋亡的关系和对胃癌预后意义。方法145例经病理证实,不同胃黏膜病变采用免疫组化检测PCNA基因表达及Warthinstarry法检测Hp感染。采用原位末端标记法(TUNEL)检测细胞凋亡。结果在浅表性胃炎(CSG)、萎缩肠化生胃炎(CAG+IM)、异型增生(DYS)、早期GC和进展期GC中,PCNA基因表达率分别为24.53%,46.28%,60.54%,57.67%和71.42%,CAG+IM、DYS、GC均显著高于CSG(P<0.05)。凋亡指数(AI)分别为(4.55±2.33)%、(6.43±5.60)%、(6.45±5.12)%、(6.55±4.80)%、(8.84±5.63)%,进展期GC显著高于CSG(P<0.05)。胃黏膜凋亡指数与PCNA表达强度有密切相关(P<0.05)。PCNA阳性表达与胃癌组织类型、浆膜浸润和淋巴结转移密切相关,而且BorrmannIV明显高于早期胃癌和BorrmannI,II(P<0.05)。PCNA阳性表达与肠型胃癌Hp感染有关。CAG+IM,DYS和GC组PCNA阳性表达中Hp感染者明显高于阴性者。Hp阳性者5年生存期显著短于Hp阴性者。结论Hp感染和PCNA表达与胃黏膜增殖和恶化有关,且与凋亡有相关性。Hp感染与胃癌预后有关。     

Association of the human leukocyte antigen class II alleles with chronic atrophic gastritis and gastric carcinoma in Koreans

OBJECTIVE: Gastric carcinogenesis is a multi‐step process and is influenced by several etiological agents, including the host's genetic factors. Since whether a patient remains with chronic superficial gastritis (CSG) or progresses to either chronic atrophic gastritis (CAG) or gastric carcinoma (GC) could be a genetic predisposition unique in each population, we hypothesized that host human leukocyte antigen (HLA) alleles could be discriminative in predicting the risk of CSG progression to precancerous CAG and GC in Koreans. METHODS: A total of 165 patients with gastric disorders (CSG, 62; CAG, 69 and GC, 34), were selected to investigate the association of HLA class II alleles with the progression of CSG to CAG or GC. HLA genotypes were obtained by the polymerase chain reaction‐sequence based typing method. RESULTS: The phenotypic frequencies of DRB1*1101 and DQA1*0505 were significantly higher in the CAG group compared to those in the CSG group. In the subjects with Helicobacter pylori (H. pypori) (+), the frequencies of DRB1*1501 and DQB1*0602 were significantly lower in the CAG compared to those in the CSG. Further analysis showed that sex (P < 0.05, OR= 0.41–0.42) and age (P < 0.05, OR= 1.05) also affected the risk of progression from CSG to CAG in H. pylori (+) patients carrying the DRB1*1501 or DQB1*0602 allele. Additionally, the frequency of DRB1*0404 in the GC group was significantly higher than that in the gastritis group. CONCLUSION: Our findings strongly imply an association between HLA class II alleles and the risk of CAG development and GC progression in Koreans.     

幽门螺杆菌相关性胃病的细胞增殖和凋亡

目的 观察幽门螺杆菌（Hp)及其CagA基因对细胞增殖和凋亡的影响,进而探讨Hp增加胃癌发生危险性的机制。方法 研究对象为慢性浅表性胃炎（CSG）、慢性萎缩性胃炎（CAG）、慢性萎缩性胃炎伴肠上皮化生（CAGIM）、不典型增生（DYS）、胃癌（GC）患者127例及正常对照组（NS）14例。应用ki-67免疫组化技术评价幽门窦上皮细胞增生,用切口末端标记法（TUNEL）检测胃上皮细胞凋亡,应用聚合酶链反应（PCR）技术检测Hp的CagA基因。结果 Hp阳性患者的增殖指数（LI）和凋亡指数（AI）显著高于Hp阴性者或正常对照（P＜0．05和P＜0．01）。CSGHp阳性的LI和AI明显高于Hp阴性者（P＜0．01）,而其余四种胃病Hp阳性患者（P＜0．05）。Hp阳性或阴性CSG、NS组的AI与LI呈正相关,GC患者的AI与LI呈负相关。LI和AI与胃粘膜炎症程度无明显关系。结论 Hp诱导胃粘膜上皮细胞过度增殖和凋亡主要发生在Hp感染的早期,CagA^ Hp与CagA^－Hp促增殖和凋亡作用的能力明显不同,Hp感染通过引起增殖和凋亡比例的失调,最终促进肿瘤发生。     

胃癌及癌前病变组织三叶因子3表达的相关性研究

目的检测三叶因子3（TFF3）在胃癌前病变及胃癌的表达,探讨TFF3的表达与胃癌发生、发展的关系。方法收集慢性浅表性胃炎（CSG）,慢性萎缩性胃炎伴中、重度肠上皮化生（IM）,慢性萎缩性胃炎伴中重度不典型增生（Dys）患者各30例,胃癌（GC）患者40例采用SP免疫组化法检测TFF3蛋白的表达。结果CSG、IM、Dys、GC组织中TFF3表达呈逐渐增强趋势,差异具有统计学意义（P〈0.05）。结论TFF3表达在胃癌发生、发展过程中起一定作用。     

胃癌与癌前病变关系的研究

目的观察胃癌（ＧＣ）的发生过程．方法在胃癌高发区山东省临朐县，对一组有胃粘膜病理诊断结果的自然人群进行随访观察，并配以嵌套式病例对照研究．结果胃粘膜肠上皮化生（ＩＭ）和异型增生（Ｄｙｓ）发生胃癌的危险性显著高于慢性萎缩性胃炎（ＣＡＧ），且在胃中不同部位的检出率与胃癌在相应部位发生的频率存在正等级相关关系；Ｄｙｓ发生胃癌所需要的时间明显短于ＩＭ发生胃癌所需要的时间．结论胃癌特别是肠型胃癌是在ＣＡＧ基础上发生ＩＭ，进而产生Ｄｙｓ，最终导致癌变的一系列过程