Abstract
SMARCB1 gene alterations were first described in highly malignant rhabdoid tumors of the kidney, brain (atypical teratoid/rhabdoid tumor) and soft tissue. An increasing number of tumors have now shown loss of SMARCB1 protein expression by immunohistochemistry, including the majority of epithelioid sarcomas. However, investigations of SMARCB1 gene alterations in epithelioid sarcoma have produced conflicting results. The aim of this study was to evaluate SMARCB1 status using Sanger sequencing of the coding region and multiplex ligation-dependent probe amplification, a rapid and sensitive method for detecting intragenic deletions and duplications, which has not been used in previous studies. Twenty-one epithelioid sarcomas of both classical and proximal type were selected for SMARCB1 gene testing and SMARCB1 immunohistochemistry. Nineteen of 21 (90%) epithelioid sarcomas were SMARCB1 negative by immunohistochemistry. Twelve of the 19 (63%) had adequate DNA recovery for evaluation. Ten of 12 (83%) tumors showed homozygous deletions of the gene. Two cases showed heterozygous deletions and polymorphisms, but no sequence mutations. These results confirm the high frequency of SMARCB1 deletions in epithelioid sarcoma and show that multiplex ligation-dependent probe amplification is a reliable method for detection of deletions in these cases, which can be performed on formalin-fixed, paraffin-embedded tissue. Given the high percentage of SMARCB1 alterations in epithelioid sarcoma, these findings argue against using SMARCB1 gene deletion as a tool in distinguishing them from malignant rhabdoid tumors.
摘要
SMARCB1基因的改变最初描述于肾脏、脑(非典型畸胎/横纹肌样肿瘤)和软组织的高度恶性横纹肌肿瘤中。通过免疫组织化学方法发现越来越多的肿瘤显示SMARCB1蛋白表达缺失,包括大部分上皮样肉瘤。然而,对上皮样肉瘤SMARCB1基因改变的研究出现了不一致的结果。本研究的目的是用编码区Sanger测序和多重连接探针扩增技术评价SMARCB1的状态,多重连接探针扩增技术是一种敏感、快速的基因缺失和倍增检测方法,在以前的研究中未曾用过。我们选定21例上皮样肉瘤(包括经典型和近端型)来做SMARCB1基因检测和SMARCB1免疫组织化学表达。21例中有19例(90%)上皮样肉瘤用免疫组织化学方法检测SMARCB1阴性。19例中12例(63%)有足够的DNA回收用于评估。12例中10例(83%)肿瘤显示基因的纯合子缺失,两例显示杂合子缺失和多态性,但是没有序列突变。这些结果证实了上皮样肉瘤的SMARCB1基因高缺失率,同时显示在这些病例中多重连接探针扩增技术检测基因缺失是一种可靠的方法,这种方法可以用于福尔马林固定、石蜡包埋的组织。考虑到上皮样肉瘤中SMARCB1高改变率,这些结果不支持用SMARCB1基因缺失做为鉴别上皮样肉瘤和恶性横纹肌肿瘤的手段。
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