过氧化物酶体增殖物激活受体γ在大肠肿瘤中的表达及意义

目的 在蛋白及mRNA水平确定过氧化物酶体增殖物激活受体γ（peroxiome proliferator activated receptor γ, PPARγ）在大肠肿瘤中的表达。方法 结肠镜下活检标本,分为正常大肠粘膜组、大肠腺瘤组及大肠癌组,免疫组化及RT PCR方法检测各组PPARγ的表达。结果 正常大肠粘膜中表达PPARγ蛋白的细胞主要是接近肠腔,分化良好的腺上皮细胞;而在大肠腺瘤中,PPARγ阳性的细胞呈弥漫分布。PPARγ蛋白及mRNA在大肠癌中的表达显著增加,明显高于大肠腺瘤和正常大肠粘膜(P<0.05)。PPARγ蛋白及mRNA在正常大肠粘膜及腺瘤中的表达无差异（P>0.05）。PPARγ mRNA在重度异型增生腺瘤中的表达高于正常大肠粘膜(P<0.05),接近于在大肠癌中的表达（P>0.05）。结论 大肠腺瘤最先发生PPARγ表达部位的变化,PPARγ在重度异型增生的大肠腺瘤及大肠癌中的表达水平较高,表明PPARγ可能在早期即参与大肠癌的发生发展。     

抗大肠癌单克隆抗体MC3的应用

大肠腺瘤异型增生是肠癌的重要癌前病变,尤其重度异型增生易发展成癌或与癌并存。在形态上重度异型增生有时又难以与高分化腺癌区别,有人认为此病变为良恶性交界性病变,因此寻找能反映恶性变的标记物对肠癌的防治是很重要的。为此,本文应用抗人大肠癌单克隆抗体MC_3对79例大肠腺瘤异型增生(轻度26例、中度39例、重度14例及可疑癌7例);34例大肠癌及5例正常大肠粘膜组织做免疫组化PAP法染色;检测肠癌相关抗原在各类肠腺瘤粘膜中异型增生不同程度中的差异及其意义做初步研究。另外,本文对肠镜活检HE原切片在免疫     

大肠癌及腺瘤细胞核中AgNOR的定量研究

本文应用AgNOR技术对10例大肠腺癌9例癌旁移行粘膜和20例大肠腺癌(绒毛状腺癌和管状腺瘤各10例)进行了AgNOR定量比较研究,另选10例大肠增生性息肉和9例大肠癌切缘“正常”粘膜作对照。结果表明:大肠癌组AgNOR颗粒数目和最大颗粒直径与绒毛状腺瘤相比无显著性差异(P>0.05),表明绒毛状腺癌高度的癌变性;管状腺瘤与绒毛状腺瘤相比有显著性差异(P<0.05),而与增生性息肉或切缘“正常”粘膜相比也有高度显著性差异(P<0.01),表明管状腺瘤与大肠癌关系不如绒毛状腺瘤密切。作者认为,AgNOR技术对大肠良恶性病变的鉴别和癌前病变的检测有重要参考价值。     

血清IGF-Ⅱ在大肠癌早期诊断中的意义

目的:研究大肠癌及大肠腺瘤患者血清中IGF-Ⅱ表达水平,探讨其在大肠癌早期诊断中的价值.方法:采用ELISA法检测13例大肠癌患者、33例大肠腺瘤患者(其中伴轻、中、重度异型增生分别为13例,11例,9例)、10例健康人血清中IGF-Ⅱ水平.结果:IGF-Ⅱ在大肠癌的阳性表达率明显高于大肠腺瘤及健康人,三组之间均有显著性差异(P<0.01).结论:IGF-Ⅱ血清含量测定可作为大肠癌早期诊断的指标.     

APC、β-catenin、C-myc和Cyclin D1在大肠癌组织中的表达及其意义

背景与目的:Wnt信号转导通路成员各癌基因、抑癌基因的异常,激活下游相关靶基因的转录,在肿瘤发生发展中起重要作用.本研究通过检测不同大肠组织中APC、β-catenin、C-myc和Cyclin D1的表达情况,探讨其在大肠癌发生中的意义.方法:应用免疫组织化学方法检测30例正常大肠粘膜、30例大肠腺瘤、10例大肠腺瘤恶变及50例大肠癌组织中APC、β-catenin、C-myc和Cyclin D1蛋白的表达情况.以β-catenin在细胞膜表达为正常表达,而在胞浆和/或胞核表达为异位表达.结果:大肠癌和大肠腺瘤恶变组织APC阳性率分别为44.0%和40.0%,显著低于大肠腺瘤(86.7%)和正常大肠粘膜(100%)(P＜0.01).大肠癌、大肠腺瘤恶变组织和大肠腺瘤β-catenin胞浆和/或胞核异位表达率分别为62.0%、50.0%、30.0%,均显著高于正常大肠粘膜(0%)(P＜0.01),大肠癌β-catenin异位表达率显著高于大肠腺瘤(P＜0.01).大肠癌、大肠腺瘤恶变组织、大肠腺瘤中C-myc表达率分别为56.0%、60.0%、46.7%,均显著高于正常大肠粘膜(0%)(P＜0.01),而Cyclin D1阳性率分别为66.0%、60.0%、30.0%,均显著高于正常大肠粘膜(0%)(P＜0.01).大肠癌Cyclin D1表达率显著高于大肠腺瘤(P＜0.01).大肠癌中β-catenin异位表达与C-myc和Cyclin D1表达呈正相关关系(r=0.63,P＜0.01;r=0.57,P＜0.01),而与APC表达呈负相关关系(r=-0.39,P＜0.05).结论:大肠癌组织中存在APC低表达和/或β-catenin异位表达,以及C-myc和Cyclin D1的过度表达,4种基因蛋白可能在大肠癌发生过程中起重要作用.     

Stat3通路相关基因在散发性大肠管状腺瘤癌变中的表达及意义

目的 探讨Stat3及CyclinD1、Bcl-xL在散发性大肠管状腺瘤癌变过程中的可能作用。方法 采用免疫组化方法检测107例散发性大肠管状腺瘤异型增生及癌变组织中Stat3和CyclinD1、Bcl-xL在蛋白水平的表达情况。结果 腺瘤伴异型增生组和癌变组中的Stat3蛋白的表达明显高于正常大肠黏膜组(P=0.000),且癌变组中Stat3蛋白的表达高于腺瘤伴异型增生组(P=0.003);腺瘤伴异型增生组和癌变组中CyclinD1蛋白的表达均明显高于正常大肠黏膜组(P=0.000),且癌变组中CyclinD1蛋白的表达高于腺瘤伴异型增生组(P=0.000);大肠管状腺瘤伴异型增生组和癌变组中Bcl-xL在蛋白水平的阳性表达率均明显高于正常大肠黏膜组（P=0.000),而且癌变组中Bcl-xL的表达明显高于腺瘤伴异型增生组(P=0.000);Stat3、CyclinD1和Bcl-xL均随腺瘤异型增生程度的增高呈递增趋势。Stat3与CyclinD1、Bcl-xL 的表达存在正相关关系。结论 Stat3、CyclinD1和Bcl-xL可能在散发性大肠管状腺瘤癌变过程中起一定的作用。     

散发性大肠管状腺瘤癌变过程中NGX6ILK和c-Jun的表达及意义

目的:探讨NGX6、ILK和c-Jun在散发性大肠管状腺瘤癌变过程中的可能作用.方法:采用免疫组化法检测22例异型增生性畸变隐窝灶(ACF)、68例大肠管状腺瘤伴上皮不同程度异型增生、21例大肠管状腺瘤癌变和21例正常对照中NGX6、ILK和c-Jun的表达情况.结果:NGX6蛋白在正常对照、异型增生性ACF、大肠管状腺瘤伴上皮异型增生及大肠管状腺瘤癌变组中阳性表达率逐步降低,而ILK蛋白和c-Jun蛋白的阳性表达率则明显升高(P<0.05).异型增生性ACF、大肠管状腺瘤伴上皮轻、中、重度异型增生组中NGX6蛋白的阳性表达率分别为77.27%、70.83%、37.50%、35.00%,其中,大肠管状腺瘤伴上皮中、重度异型增生组中NGX6蛋白的阳性表达率明显低于异型增生性ACF及腺瘤伴上皮轻度异型增生组(P<0.05).异型增生性ACF、大肠管状腺瘤伴上皮轻、中度异型增生组中ILK蛋白的阳性表达率明显低于腺瘤伴上皮重度异型组(P<0.05);c-Jun蛋白阳性表达率在大肠管状腺瘤伴上皮轻、中、重度异型增生和大肠管状腺瘤癌变组明显高于异型增生性ACF(P<0.05).在大肠管状腺瘤癌变过程中NGX6和ILK间呈负相关(r=-0.455,P<0.05);NGX6和c-Jun间呈负相关(r=-0.417,P<0.05);ILK和c-Jun之间呈正相关(r=0.390,P<0.05).结论:NGX6低表达可能与ILK及c-Jun高表达有关,这可能在散发性大肠管状腺瘤形成及癌变过程中发挥一定作用.     

表皮生长因子受体在大肠癌及癌前病变组织中的研究

用抗表皮生长因子受体（ＥＧＦＲ）的单抗和免疫组化ＡＢＣ法，对正常大肠粘膜，大肠腺瘤伴异型增生及大肠腺癌进行标记，发现正常大肠粘膜全部为阴性，大肠腺瘤伴异型增生则有较高的表达率，而一旦癌变后，表达率有所下降，ＥＧＦＲ的表达与大肠腺癌的低分性及高浸相关，ＥＧＦＲ表达的肿瘤易发生淋巴结转移，研究结果提示，ＥＧＦＲ的表达与大肠癌的发生有一定关系，并可作为判断大肠癌生物学行为的一个有用指标。     

热休克蛋白10在大肠癌发生发展中的表达及其意义

目的了解热休克蛋白10（HSP10）在正常大肠粘膜、腺瘤和腺癌中的表达,并探讨其与大肠癌发生发展的关系.方法应用免疫组化Envision二步法,观察HSP10在正常大肠粘膜、腺瘤和腺癌中的表达,并比较其间是否存在差异.结果 HSP10在大肠腺瘤、腺癌中的阳性表达程度高于正常大肠粘膜（P〈0.001）;HSP10在不同程度不典型增生的大肠腺瘤、不同分化程度与淋巴结转移状态大肠腺癌中呈阳性至强阳性表达,统计学分析结果表明差异无显著性意义（P〉0.05）.结论提示HSP10与大肠癌的发生发展有关,有可能成为检测大肠癌的早期诊断标志物;HSP10的表达与大肠腺瘤的不典型增生程度和大肠癌的分化程度、淋巴结转移状态无关.     

鼠实验性大肠癌Ag—NOR计数变化

本文在建立二甲肼(DMH)大鼠大肠癌模型的基础上,用核仁组成区嗜银蛋白(Ag—NOR)银染技术对68例大肠粘膜标本进行了研究。标本包括15例正常结肠粘膜、10例轻度不典型增生;13例中度不典型增生和30例大肠癌。结果显示大肠癌细胞核中AgNORs计数(6.29±1.5)明显增多,显著高于其它各组(P<0.01)。中度不典型增生细胞核内AgNOR平均计数为3.07±0.42,亦高于正常组(1.57±0.16)及轻度不典型增生组(1.81±0.21),P<0.01。正常组与轻度不典型增生组AgNOR计数无显著性差异(P>0.05)。这些结果提示Ag—NOR定量计数,可作为光镜水平下辅助判断大肠良恶性病变有用指标。     

PROLIFERATION RATE OF COLONIC NEOPLASMS AND MUCOSA ADJACENT TO NEOPLASMS: IMMUNOHISTOCHEMICAL STUDY

Biopsy specimens of normal mucosa (n=5). adenomas (n -13), adenocarcinomas (n = 8). mucosa adjacent to adenoma (n=10) mucosa adjacent to adenocarcinoma (n = 7 ) at the large bowel were investigated by an iminunohistochemical method using 5- bromodeoxynldine (BrdUrd) . The labeling index (LI) was significantly lower in normal nucosa than mucosa adjacent to neoplasms and adenomas and adenocarcinomas. The proliferative zone was confined to the lower two- third at the crypt in normal mucosa and in mucosa adjacent to neoplasms. The labeled cells were either present in the upper third or scattered along the crust and in surface epithelium. The results support the adenmo-carcinoma sequence.     

Cell kinetic indicators of premalignant stages of colorectal cancer

Using an in vitro double labeling technique with two different levels of 3H-thymidine, the duration of the phase of DNA synthesis (S) and the labeling index (LI) were measured in the colorectal mucosa of three groups of patients: patients with colorectal neoplasms (adenomas and/or adenocarcinomas), patients with inflammatory bowel disease, and a control group of patients without gastrointestinal pathology. In those patients with colorectal neoplasms, samples were obtained from both the neoplastic mucosa and from the normal appearing mucosa at various distances from the lesions. One-way analyses of variance were used to test the equality of mean S-phase duration and LI in the various types of tissues. S-phase duration was significantly longer in the tumor than in the unaffected mucosa of patients with adenocarcinoma (18.65 hours +/- 2.3 versus 10.13 hours +/- 1.26 P less than 0.0001). However, S-phase duration was significantly longer in the unaffected mucosa of cancer patients than in the mucosa of patients without gastrointestinal pathology (10.58 hours +/- 1.84 versus 7.91 hours +/- 0.46, P = 0.013). Similarly, LI was significantly higher in the unaffected mucosa of patients with adenoma and adenocarcinoma than in the mucosa of patients without gastrointestinal pathology (19.1% +/- 3.0 versus 9.5% +/- 2.2, P less than 0.0001). There was a highly significant trend to a progressive increase of LI from flat histologically normal appearing mucosas to inflammatory mucosas, adenomas, and adenocarcinomas (P less than 0.0001). These results suggest that increased S-phase duration is specifically related to cancer. In mucosa without histologic sign of malignancy, an increased S-phase duration would indicate that the malignant process has started. An increased LI would appear to relate to the selective advantage that rapidly proliferating cells hold over less proliferating ones.     

Increased expression of RelA/nuclear factor-kappa B protein correlates with colorectal tumorigenesis

OBJECTIVE: To identify the role of RelA/nuclear factor-kappa B, an important inhibitor of apoptosis in colorectal tumorigenesis, we examined the expression of RelA in normal colorectal mucosa (n = 10), colorectal adenomas (n = 30) and colorectal adenocarcinomas (n = 30). Furthermore, the association of RelA expression with tumor cell apoptosis, proliferation, and expression of Bcl-2/Bcl-x(L )was also studied. METHODS: Paraffin sections were stained with monoclonal antibodies directed against RelA, Bcl-2, Bcl-x(L), and Ki-67 to assess protein expression patterns in normal, adenomatous and colon cancer tissue. Apoptotic cells were detected by terminal deoxynucleotidyl-transferase-mediated dUTP-biotin nick end labeling (TUNEL) using an in situ detection kit. RESULTS: The results of immunohistochemical staining revealed that expression of RelA, Bcl-2, Bcl-x(L), and Ki-67 labeling index (LI) significantly increased in the transition from adenoma with low dysplasia to adenocarcinoma. This transition was associated with a significant decrease in the apoptotic index (AI) and a significant increase in the Ki-67 LI. The expression of RelA correlated inversely with the AI and correlated positively with the expression of Bcl-2, Bcl-x(L), and Ki-67 LI in the transition from low-grade dysplasia to adenocarcinoma. CONCLUSION: Our results suggest that increased expression of RelA/nuclear factor-kappa B plays an important role in the transition from colorectal adenoma with low-grade dysplasia to adenocarcinoma in the pathogenesis of colon cancer in humans.     

Abnormalities in the expression of cell cycle-related proteins in tumors of the small bowel.

Tumors of the small bowel are quite rare for unknown reasons, although they resemble colorectal tumors in many respects. The purpose of this study was to determine whether abnormalities in the expression of several cell cycle control genes are of importance in small bowel tumorigenesis by comparing a series of samples of normal mucosa, adenomatous polyps, and adenocarcinomas. The levels of cyclin D1, cyclin E, p16, p21, p27, and p53 proteins were determined by immunohistochemistry in samples of normal small bowel (n = 16), small bowel adenomas (n = 20), and small bowel adenocarcinomas (n = 24). Normal small bowel mucosa expressed p27 protein, but not the other cell cycle-related proteins. About 20% of the tumors displayed a decrease in the expression of this protein. The most frequent alteration in the tumors was an increase in the p16 protein. Increased expression of p53 was associated with tumor progression because it was overexpressed in 45% of the adenomas and 65% of the adenocarcinomas (P<0.05). Advanced age and increased detection of cyclin D1 and p53 were associated with a decreased 3-year survival (P<0.05). Cell cycle abnormalities are early and important events in the multistep process of small bowel tumorigenesis, thus resembling colorectal carcinogenesis. As in colon cancer, deregulated expression of G1 proteins may perturb cell cycle control in benign adenomas of the small bowel and thereby enhance tumor progression. Increased expression of cell cycle inhibitors in tumors may serve as a defense mechanism for tumor progression.     

Matrix Metalloproteinase-9 Expression in the Normal Mucosa–Adenoma–Dysplasia–Adenocarcinoma Sequence of the Colon

It has been proposed that matrix metalloproteinases (MMPs) play a role in tumor invasion. We determined protein expression of matrix metalloproteinase-9 (MMP-9) in colorectal cancer (CRC), corresponding normal mucosa and colorectal adenomas. For confirmation of immunohistochemical results MMP-9 TaqMan RT-PCR analysis was performed. Expression of MMP-9 was determined on paraffin embedded biopsy sections by immunohistochemistry in 31 CRC patients (from cancer tissue and corresponding normal mucosa) and in 30 patients with adenoma (nine adenomas with high grade of dysplasia). MMP-9 immunostaining was determined semi-quantitatively. For Taqman RT-PCR analyses normal mucosa (n = 5), adenoma without (n = 6) and with high grade dysplasia (n = 7) and CRC (n = 10) were investigated. Statistical analysis with ANOVA, LSD test and correlation analysis were performed. P value of <0.05 was considered significant. The MMP-9 expression in CRC was significantly higher compared to adenomas or the normal mucosa (P = 0.001). Significantly higher expression of MMP-9 has been observed in adenomas with high grade dysplasia compared to other adenomas or normal colon (P < 0.001). Diffuse strong MMP-9 expression was present in tumor as well as in stromal cells. In adenoma samples, dysplastic epithelial cells showed moderate intensive cytoplasmic MMP-9 expression, with a clear-cut differentiation between dysplastic and non-dysplastic areas. Staining intensity correlated with the grade of CRC. We demonstrate a significantly higher expression of MMP-9 in adenoma with high grade dysplasia-CRC sequence as compared to normal tissue. The over-expression of MMP-9 strongly suggests its association with colorectal carcinogenesis.     

Progression of tumors arising from large ACF is associated with the MUC5AC expression during rat colon MNNG carcinogenis

Aberrant crypt foci (ACF) are microscopic lesions which have been postulated to precede the development of adenomas, precursors of colon cancer. The gastric M1/MUC5AC mucin has also been described as an early marker of colon carcinogenesis in the human and in the rat. To study changes in mucin expression associated with the genesis of tumors, Wistar rats were treated by intrarectal instillations of MNNG, twice a week for 2 weeks, and were sacrificed 10 (n = 20), 14 (n = 20), 22 (n = 20), 30 (n = 10) and 66 (n = 16) weeks after the beginning of the treatment. In the treated rats, the MUC5AC mucin was mainly expressed in ACF compared with the histologically normal mucosae, which showed few isolated MUC5AC-positive normal crypts. During carcinogenesis, the percentage of large ACF [> or =10 aberrant crypts] increased and the number of MUC5AC-positive (NCs) decreased. At Week 30, small tumors were observed arising from large ACF, both types of lesions expressing MUC5AC. At Week 66, large tumors showed remnants of MUC5AC-positive ACF in their adjacent mucosae. This observation suggests that the expression of MUC5AC is associated with the ACF/adenoma sequence and supports the notion of large ACF as precursors of adenomas/adenocarcinomas. Moreover, the expression of MUC5AC in the transitional mucosa adjacent to both rat and human colon tumors suggests that some human tumors could arise from large ACF, and reinforces the concept of the premalignant potential of these lesions.     

JC virus infection in colorectal neoplasia that develops after liver transplantation

PURPOSE: Liver transplant recepients (LTRs) have an increased risk of colorectal neoplasia. The mechanism responsible for this is unknown. JCV encodes for TAg and has been implicated in colorectal carcinogenesis. We hypothesized that the use of immunosuppression in LTRs facilitates activation of JCV and is responsible for the increased risk of neoplasia. EXPERIMENTAL DESIGN: JCV TAg DNA and protein expression were determined in normal colonic epithelium (n = 15) and adenomatous polyps (n = 26) from LTRs and compared with tissue samples from control patients (normal colon, n = 21; adenomas, n = 40). Apoptosis and proliferation were determined by M30 and Ki-67 immunoreactivity, respectively. RESULTS: JCV TAg DNA was found in 10 of 15 (67%) of normal colonic mucosa from LTRs compared with 5 of 21 (24%) of control normal mucosa (P = 0.025). JCV TAg DNA was detected in 16 of 26 (62%) of the adenomas from LTRs and in 20 of 40 (50%) of control adenomas. JCV TAg protein was expressed in 13 of 26 (50%) adenomas from LTRs versus 2 of 40 (5%) of adenomas from controls (P < 0.001). In adenomas from LTRs, the mean proliferative activity was higher compared with controls (60.3 +/- 3.2% versus 42.7 +/- 2.8%, P < 0.001), whereas mean apoptotic indices were lower in LTRs (0.29 +/- 0.08% versus 0.39 +/- 0.06%, P = 0.05). CONCLUSIONS: The presence of JCV in the colorectal mucosa and adenomas from LTRs, in concert with the use of immunosuppressive agents, suggests that JCV may undergo reactivation, and the subsequent TAg protein expression might explain the increased risk of colorectal neoplasia in LTRs.     

大肠肿瘤中bcl—2及PCNA表达及其意义

目的：研究ｂｃｌ－２及ＰＣＮＡ在大肠肿瘤肆生中的作用及其临床意义。方法：应用免疫组化Ｓ－Ｐ法分别检测大肠正常粘膜、腺瘤及腺癌中ｂｃ；－２及ＰＣＮＡ表达。结果：Ｂｃｌ－２在正常粘膜基底部上皮细胞表达，在腺瘤（７７．５％）和腺癌中（５６．３％）ｂｃｌ－２表达差异显（Ｐ〈０．０５）。高分化腺癌ｂｃｌ－２表达率（６８．４％）显高于差分化腺癌（４１．７％），ＰＣＮＡ表达在正常粘膜，腺瘤及腺癌中依次递增，     

Frequent CpG island methylation in precursor lesions and early gastric adenocarcinomas

Gastric carcinogenesis involves multiple genetic and epigenetic alterations. Epigenetic silencing of tumor-related genes due to CpG island methylation (CIM) has been recently reported in gastric cancer, but the role in precursor lesions is not well understood. We analysed the methylation status of the tumor suppressor gene p16, the DNA mismatch repair gene hMLH1, and four CpG islands (MINT1, MINT2, MINT25, and MINT31) using methylation-specific polymerase chain reaction in 35 polypoid adenomas and 46 flat dysplasias unassociated with carcinoma, 34 early adenocarcinomas (T1N0M0) and associated adenomas/dysplasias, and corresponding adjacent non-neoplastic mucosa. The extent of CIM was defined by the fraction of methylated loci (methylation index), and compared with previously characterized genetic alterations (microsatellite instability (MSI) and APC gene mutation). We found that methylation of p16 was more frequent in adenocarcinoma-associated dysplasias/adenomas (29%) and adenocarcinomas (44%) as compared to flat dysplasias (4%) and adenomas (18%) unassociated with adenocarcinoma (P=0.001). The mean methylation index increased from normal/chronic gastritis (CG) mucosa (0.09) to intestinal metaplasia (IM) (0.16), flat dysplasias (0.40) or polypoid adenomas (0.41) unassociated with carcinoma, dysplasias/adenomas associated with carcinoma (0.44), and adenocarcinomas (0.44). There was no difference in frequencies of high-level CpG island methylation (CIM-H, methylation index > or =0.5) among flat dysplasias (50%) and polypoid adenomas (51%) unassociated with carcinoma, dysplasias/adenomas associated with adenocarcinoma (47%), and adenocarcinoma (47%). CIM-H was present in 15% of IM, but not in normal/CG mucosa. There was a significant correlation between methylation of hMLH1 and high-level of microsatellite instability (MSI-H): methylation of hMLH1 was present in 71% of MSI-H tumors, but only 8% of MSI-low tumors and 13% of microsatellite-stable tumors (P=0.0001). There was no statistical difference between methylation index and APC mutation. Our results indicate that concurrent promoter methylation is an early and frequent event in gastric tumorigenesis, including both MSI-H and microsatellite-stable neoplasms. Methylation of the p16 gene may contribute to the malignant transformation of gastric precursor lesions.