Abstract：
A subset of head and neck squamous cell carcinomas present solely as metastatic disease in the neck and are of unknown primary origin (SCCUP). Most primary tumors will ultimately be identified, usually in the oropharynx. In a minority of cases, the primary site remains elusive. Here, we examine the role of ancillary testing, including mutational signature analysis (MSA), to help identify likely primary sites in such cases. Twenty-two cases of SCCUP in the neck, collected over a 10-year period, were classified by morphology and viral status; including human papillomavirus (HPV) testing by p16 immunohistochemistry (IHC) and RT-qPCR, as well as Epstein-Barr virus (EBV) testing by EBER-ISH. CD5 and c-KIT (CD117) IHC was done to evaluate for possible thymic origin in all virus-negative cases. Whole exome sequencing, followed by MSA, was used to identify UV signature mutations indicative of cutaneous origin. HPV was identified in 12 of 22 tumors (54.5%), favoring an oropharyngeal origin, and closely associated with nonkeratinizing tumor morphology (Fisher\'s exact test; p = 0.0002). One tumor with indeterminant morphology had discordant HPV and p16 status (p16+/HPV-). All tumors were EBV-negative. Diffuse expression of CD5 and c-KIT was identified in 1 of 10 virus-negative SCCUPs (10%), suggesting a possible ectopic thymic origin rather than a metastasis. A UV mutational signature, indicating cutaneous origin, was identified in 1 of 10 (10%) virus-negative SCCUPs. A cutaneous auricular primary emerged 3 months after treatment in this patient. Primary tumors became clinically apparent in 2 others (1 hypopharynx, 1 hypopharynx/larynx). Thus, after follow-up, 6 tumors remained unclassifiable as to the possible site of origin (27%). Most SCCUPs of the neck in our series were HPV-associated and thus likely of oropharyngeal origin. UV signature mutation analysis and additional IHC for CD5 and c-KIT for possible thymic origin may aid in further classifying virus-negative unknown primaries. Close clinical inspection of hypopharyngeal mucosa may also be helpful, as a subset of primary tumors later emerged at this site.
摘要：
头颈部鳞状细胞癌的一个子集仅表现为颈部转移性疾病，并且原发不明（SCCUP）。大多数原发性肿瘤最终将被识别，通常在口咽部。在少数情况下，主要网站仍然难以捉摸。这里,我们研究辅助测试的作用，包括突变特征分析(MSA)，以帮助识别在这种情况下可能的主要网站。22例颈部SCCUP,收集了10年的时间，通过形态学和病毒状态进行分类;包括通过p16免疫组织化学（IHC）和RT-qPCR检测人乳头瘤病毒（HPV），以及EBER-ISH的爱泼斯坦-巴尔病毒（EBV）测试。进行CD5和c-KIT（CD117）IHC以评估所有病毒阴性病例中可能的胸腺起源。全外显子组测序,其次是MSA，用于鉴定指示皮肤起源的UV特征突变。在22个肿瘤中的12个（54.5%）中发现了HPV，有利于口咽起源，与非角质化肿瘤形态密切相关（Fisher精确检验；p=0.0002）。一个具有不确定形态的肿瘤具有不一致的HPV和p16状态(p16+/HPV-)。所有肿瘤均为EBV阴性。在10个病毒阴性SCCUP中的1个（10％）中鉴定出CD5和c-KIT的弥漫性表达，提示可能是异位胸腺起源而不是转移。紫外线突变特征，表明皮肤起源，在10个(10%)病毒阴性SCCUP中的1个中鉴定。该患者在治疗后3个月出现皮肤耳廓原发性。原发性肿瘤在另外2个临床上变得明显（1个下咽，1下咽/喉）。因此，随访后,6个肿瘤对于可能的起源部位仍然无法分类(27%)。在我们的系列中，大多数颈部的SCCUP与HPV相关，因此可能是口咽部起源。针对可能的胸腺起源的CD5和c-KIT的UV特征突变分析和额外的IHC可能有助于进一步分类病毒阴性未知的原发性。密切下咽粘膜的临床检查也可能有帮助，作为原发性肿瘤的一个子集，后来出现在这个部位。
