Abstract：
Morphological overlap exists between cutaneous granular cell tumours (GCT) and malignant melanoma, with the melanocyte-specific markers HMB45 and Melan-A commonly used to support the diagnosis of melanoma. We recently encountered several cases of GCT in our practice showing strong expression of Melan-A. The aim of this study was to establish the prevalence of positive immunohistochemical staining for Melan-A and HMB45 in a series of unequivocal GCTs. We also aimed to assess the prevalence of staining for PRAME (PReferentially expressed Antigen in MElanoma), a marker expressed in >80% of primary melanomas as well as many non-melanocytic tumours. A total of 20 cutaneous/subcutaneous GCTs were evaluated using Melan-A, HMB45 and PRAME immunohistochemistry. Staining for Melan-A and HMB45 was scored using a semiquantitative scale from 0 (absent) to 3+ (staining present in >50% of tumour cells). PRAME expression was recorded as either positive (>75% of cell nuclei staining) or negative. Melan-A expression was observed in four GCTs (20%), with strong and diffuse (3+) staining seen in two cases (10%), both from anogenital areas. Weak patchy nuclear PRAME expression was seen in every case, interpreted to be negative. HMB45 was also negative in all cases (100%). Our study demonstrates that Melan-A expression can be strong and diffuse in a subset of otherwise unequivocal cutaneous GCTs, which may cause diagnostic confusion with malignant melanoma. HMB45 and PRAME did not stain any of the GCTs in our series.
摘要：
皮肤颗粒细胞瘤（GCT）和恶性黑色素瘤之间存在形态重叠，黑素细胞特异性标志物HMB45和Melan-A通常用于支持黑色素瘤的诊断。我们最近在实践中遇到了几例GCT，显示出Melan-A的强烈表达。这项研究的目的是确定一系列明确的GCTs中Melan-A和HMB45的阳性免疫组织化学染色的患病率。我们还旨在评估PRAME（MElanoma中PReferential表达的抗原）染色的患病率，在>80％的原发性黑色素瘤以及许多非黑素细胞肿瘤中表达的标志物。使用Melan-A评估了总共20个皮肤/皮下GCT，HMB45和PRAME免疫组织化学。使用从0(不存在)到3+(染色存在于>50%的肿瘤细胞中)的半定量标度对Melan-A和HMB45的染色进行评分。PRAME表达记录为阳性(>75%的细胞核染色)或阴性。在四个GCTs（20％）中观察到Melan-A表达，2例（10％）可见强烈和弥漫性（3+）染色，都来自肛门生殖器区域。在每种情况下都可以看到微弱的斑片状核PRAME表达，被解释为消极的。HMB45在所有情况下也是阴性的(100%)。我们的研究表明，Melan-A的表达可以在其他明确的皮肤GCTs的子集中强烈和扩散，这可能会导致恶性黑色素瘤的诊断混乱。HMB45和PRAME没有染色我们系列中的任何GCT。
