Division of Laboratory Genetics and Genomics, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota.
Division of Anatomic Pathology, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota.
J Natl Compr Canc Netw. 2023 Aug;21(8):787-791. doi: 10.6004/jnccn.2023.7014.
A 74-year-old male presented with rectal pain; workup uncovered an anal mass, and a diagnosis of melanoma was rendered via histologic examination and immunohistochemical (IHC) studies. Droplet digital PCR (ddPCR)-based BRAF testing was performed and revealed the presence of BRAF V600E, which is a common targetable genetic alteration in melanoma. Interestingly, the ratio of mutant to wild-type copy number was low (0.3%), whereas tumor cell percentage on tissue slides was 90%. With additional workup, BRAF V600E IHC confirmed a very small subset of BRAF V600E-positive cells, and a next-generation sequencing (NGS) panel revealed a pathogenic KIT variant, p.L576P, with an allele frequency of 63%. It was initially hypothesized that the main driver of the melanoma was the KIT alteration, whereas a small subclone (not detected by NGS, which has a 5% limit of detection) was driven by the BRAF V600E detected by ddPCR. To determine whether there were morphologic differences between the 2 clones, a careful review of the histology was performed and revealed distinct morphology of the BRAF V600E-positive cells, including pale cytoplasm, nuclear grooves, and infiltrating eosinophils. Additional IHC workup of the BRAF V600E-positive cells showed coexpression of CD1a, Langerin, and S100, diagnostic of Langerhans cell histiocytosis (LCH). This diagnosis was unexpected and would have been missed without highly sensitive molecular testing; yet it is of clinical importance for the patient. This case raises interesting biology questions regarding the relationship between melanoma and LCH; moreover, it highlights the importance of integrating quantitative information in molecular data interpretation.
一位 74 岁男性出现直肠疼痛；通过检查发现了一个肛门肿块，并通过组织学检查和免疫组织化学（IHC）研究诊断为黑色素瘤。进行了基于液滴数字 PCR（ddPCR）的 BRAF 检测，结果显示存在 BRAF V600E，这是黑色素瘤中常见的可靶向遗传改变。有趣的是，突变型与野生型拷贝数的比例较低（0.3%），而组织切片上的肿瘤细胞百分比为 90%。通过进一步检查，BRAF V600E IHC 证实了一小部分 BRAF V600E 阳性细胞，下一代测序（NGS）面板显示存在致病性 KIT 变体 p.L576P，其等位基因频率为 63%。最初的假设是，黑色素瘤的主要驱动因素是 KIT 改变，而一小部分亚克隆（未被 NGS 检测到，其检测限为 5%）则由 ddPCR 检测到的 BRAF V600E 驱动。为了确定这 2 个克隆之间是否存在形态学差异，对组织学进行了仔细检查，结果显示 BRAF V600E 阳性细胞具有明显的形态学特征，包括淡染的细胞质、核沟和浸润的嗜酸性粒细胞。对 BRAF V600E 阳性细胞进行的额外 IHC 检测显示 CD1a、Langerin 和 S100 的共表达，诊断为朗格汉斯细胞组织细胞增生症（LCH）。如果没有高度敏感的分子检测，这种诊断是出乎意料的，也会被遗漏；但对患者来说具有重要的临床意义。该病例提出了有关黑色素瘤和 LCH 之间关系的有趣生物学问题；此外，它强调了在分子数据分析解释中整合定量信息的重要性。
