后肾腺瘤的分子遗传学特征及鉴别诊断

Molecular features of metanephric adenoma and their values in differential diagnosis

目的：研究后肾腺瘤的分子遗传学特征及其鉴别诊断。方法运用特异性抗体VE1，采用免疫组织化学法检测21例后肾腺瘤、16例上皮为主型肾母细胞瘤（ e-WT）和20例实体为主型乳头状肾细胞癌（ s-PRCC）中BRAF V600E突变蛋白和p16蛋白的表达情况，并将BRAF V600E免疫组织化学与Sanger测序法比较，同时应用荧光原位杂交技术（ FISH）检测3种肿瘤中第7号和第17号染色体的异常。结果21例后肾腺瘤中有14例（66.7％） BRAF V600E突变蛋白呈弥漫、中到强的颗粒状胞质阳性，并且首次在16例e-WT中检测到2例（2／16）表达BRAF V600E突变蛋白，而20例s-PRCC均为阴性（ P＜0.05）。 Sanger 测序法证实所有BRAF V600E免疫组织化学染色阳性的病例（包括14例后肾腺瘤和2例e-WT）均存在BRAF V600E突变，未检测到BRAF V600E免疫组织化学阴性病例突变。21例后肾腺瘤中各有1例分别存在第7号染色体三倍体（4.8％）和第17号染色体三倍体（4.8％），16例e-WT中仅发现2例（2／16）第17号染色体三倍体，而20例s-PRCC中分别有2例（10.0％，2／20）、3例（15.0％，3／20）、14例（70.0％，14／20）出现第7号染色体三倍体、第17号染色体三倍体以及第7号、第17号染色体同时三倍体。后肾腺瘤、e-WT、s-PRCC中第7号和／或17号染色体三倍体的总阳性率分别为9.6％（2／21）、2／16、95.0％（19／20）。 p16蛋白在81.0％（17／21）的后肾腺瘤中呈阳性，而在e-WT和s-PRCC中的阳性率仅为2／16和5.0％（1／20）。结论大多数后肾腺瘤存在BRAF V600E突变，后肾腺瘤中少见PRCC特征性的第7号、第17号染色体三倍体异常，这些分子遗传学特征有助于后肾腺瘤与具有相似形态学的肾脏肿瘤的鉴别；特异性抗体VE1可用于肾脏肿瘤中BRAF V600E突变的筛查；p16蛋白在后肾腺瘤中高表达，后肾腺瘤的低增殖率可能与由p16介导的、BRAF基因突变诱导的细胞衰老有关。

Objective To study the molecular features of metanephric adenoma （ MA） and discuss their values in differential diagnosis .Methods BRAF V600E immunohistochemistry （ IHC） using the mutation-specific VE1 monoclonal antibody and Sanger sequencing of BRAF mutations were performed on 21 MAs, 16 epithelial-predominant Wilms tumors （ e-WT） and 20 the solid variant of papillary renal cell carcinomas （ s-PRCC ） respectively.p16 protein was detected by IHC also.Fluorescence in situ hybridization （ FISH） analyses using centromeric probes for chromosome 7 and 17 were performed on the three renal tumors in parallel.Results Fourteen （14/21,66.7%） of 21 MA cases demonstrated diffuse , moderate to strong cytoplasmic BRAF V600E IHC staining and the BRAF V600E protein expression was detected in 2 （2/16） of 16 e-WT cases for the first time, whereas all s-PRCCs were negative （P〈0.05）. All cases （including 14 MAs and 2 e-WTs） with diffuse, moderate to strong cytoplasmic BRAF V600E IHC staining were confirmed to harbor BRAF V600E missense mutations using Sanger sequencing , and no BRAF＆nbsp;mutations were detected in cases with negative BRAF V 600E protein expression.One case （1/21,4.8%） showed trisomy of chromosome 7 alone, and another one （1/21,4.8%） showed trisomy of chromosome 17 alone in 21 MAs.Two cases （ 2/16 ） of 16 e-WTs showed trisomy of chromosome 17 alone.In 20 s-PRCCs, trisomy of chromosomes 7 alone was reported in 2 cases （2/20）, trisomy of chromosome 17 alone in 3 cases （3/20） and trisomy of chromosome 7 and 17 in 14 cases （14/20）.The total positive rates of trisomy of chromosome 7 and/or 17 in MAs, e-WTs and s-PRCCs were 9.6% （2/21）, 2/16 and 95.0%（19/20）.p16 protein was positive in 81.0% （17/21） MAs, whereas the positive rates in e-WTs and s-PRCCs were 2/16 and 5.0% （1/20）.Conclusions Most MAs harbor BRAF V600E mutations, and MAs lack the gains of chromosome 7 and 17 that are characteristic of papillary renal cell carcinoma.These molecular features can be used to distinguish MA from its mimics.BRAF V600E IHC using the mutation-specific VE1 monoclonal antibody provides an effective method in BRAF V 600E mutations detection of renal tumors.p16 is overexpressed in MA , and the finding suggests that the low proliferative rate of the tumor might be attributed to BRAF V600E-induced senescence mediated by p 16.