默克尔细胞癌 (MCC) 是一种罕见的皮肤癌，90% 以上的病例发生在头颈部区域。 MCC 是一种侵袭性疾病，在免疫疗法出现之前预后不佳。 Avelumab 是一种抗 PDL1 药物，在表现出高缓解率和对生存的有利影响后，自 2017 年起被批准用于治疗晚期 MCC。从初始诊断开始对原发性肿瘤活检进行下一代测序 (NGS)（Foundation One CDx、罗氏诊断） ）以及在 avelumab 治疗之前和治疗期间获得的血浆样本（Foundation One Liquid，Roche Diagnostics）。我们介绍了一名患有转移性 MCC 的患者的病例，该患者在 80 个月的时间里在左腮腺/耳前区域发生了转移性 MCC具有长期高紫外线暴露史的 3 岁男性。在使用 avelumab 10 mg/kg/q2wk 两个周期后，几乎完全代谢反应和主要放射学反应发生，同时 ctDNA 肿瘤分数以及在治疗前检测到的所有突变的变异等位基因频率 (VAF) 迅速减少。开始使用 avelumab。Avelumab 可能在转移性 MCC 中实现快速且显着的缓解。我们的研究表明，ctDNA 反映了放射学反应，可以作为 MCC 诊断和疾病监测的理想伴侣。版权所有 © 2024 Elsevier Ltd。保留所有权利。

Merkel cell carcinoma (MCC) is an uncommon skin cancer that in more than 90 % of cases develops within the head and neck region. MCC is an aggressive disease with a dismal prognosis before the advent of immunotherapy. Avelumab, an anti-PDL1 agent is approved since 2017 for the treatment of advanced MCC after demonstrating a high response rate and favorable impact in survival.Next generation sequencing (NGS) of the primary tumor biopsy from initial diagnosis (Foundation One CDx, Roche Diagnostics) as well as from plasma samples (Foundation One Liquid, Roche Diagnostics) obtained before and during treatment with avelumab were performed.We present the case of a patient with a metastatic MCC developing in the left parotid gland / pre-auricular area in an 80-year-old male with a long-lasting history of high UV exposure. After two cycles of avelumab 10 mg/kg/q2wk a near complete metabolic response and a major radiological response occurred in parallel to a brisk reduction in the ctDNA tumor fraction as well as variant-allele frequencies (VAFs) of all the mutations detected before the start of avelumab.Avelumab may achieve rapid and major responses in metastatic MCC. Our study demonstrates that ctDNA mirrors radiological responses and may serve as an ideal companion for diagnosis and disease monitoring in MCC.Copyright © 2024 Elsevier Ltd. All rights reserved.