St John's Institute of Dermatology, Guy's and St Thomas' NHS Trust, London, UK.
Centre Léon Bérard, Lyon, France.
Pathology. 2022 Aug;54(5):541-547. doi: 10.1016/j.pathol.2021.12.293. Epub 2022 Mar 26.
Melanocytic lesions in the nail apparatus are often challenging. Both subungual melanomas (SUM) and blue naevus of the nail are very rare. Occasionally, melanomas may mimic blue naevus histologically. Benign and malignant blue melanocytic lesions are commonly associated with G protein mutations, a distinct abnormality not associated with conventional subungual melanomas. We describe the clinical, histological and immunohistochemical features of nine cases of SUM with blue naevus-like morphological features. Mutations in exon 4 and 5 of GNAQ and GNA11 were investigated in two cases, which showed no mutations. RNA-seq of one case revealed unknown mutations along with mutations in ATM, METK and ARID1A. Our study delineates a variant of SUM that mimics blue naevus. Awareness of this pitfall is important when evaluating heavily pigmented lesions around the nail in order to avoid misdiagnosis. Appropriate sampling of subungual lesions and clinicopathological correlation are paramount to reach the correct diagnosis.
甲黑素细胞病变常具挑战性。甲下黑素瘤（SUM）和甲蓝痣均非常罕见。偶尔，黑素瘤在组织学上可能类似甲蓝痣。良性和恶性蓝黑素细胞病变通常与 G 蛋白突变相关，这是一种与传统甲下黑素瘤无关的明显异常。我们描述了 9 例具有甲蓝痣样形态特征的 SUM 的临床、组织学和免疫组化特征。对两例病例进行了 GNAQ 和 GNA11 外显子 4 和 5 的突变检测，结果未发现突变。一例病例的 RNA-seq 显示存在未知突变，同时还存在 ATM、METK 和 ARID1A 突变。我们的研究描绘了一种模拟甲蓝痣的 SUM 变体。在评估甲周围色素沉着严重的病变时，了解这一陷阱非常重要，以避免误诊。对甲下病变进行适当的取样并进行临床病理相关性分析至关重要，以做出正确的诊断。
