Background: Anal squamous-cell carcinoma (ASCC) is a rare cancer. Immune checkpoint inhibitors (ICIs) are used as a second-line treatment. We aimed to analyze the genomic and transcriptomic profiles of ASCC to predict ICI efficacy.

Materials and methods: Next-generation sequencing (NGS) of DNA and RNA was carried out. Programmed death- ligand 1 (PD-L1) expression was tested by immunohistochemistry (IHC) as high (≥2+ and ≥5%), low (1-2+ and ≥1%), and negative (<1). Deficient mismatch repair/microsatellite instability-high (dMMR/MSI-H) was tested using IHC/NGS, and tumor mutation burden-high (TMB-H) was defined as ≥10 mutations/Mb. quanTIseq was used to quantify tumor microenvironment. The chi-square test / Fisher's exact test was used, and significance was determined as P value adjusted for multiple comparisons (q < 0.05). Real-world overall survival and time on treatment (TOT) were obtained from insurance claims.

Results: Out of 1242 tumor samples, 64.25% expressed PD-L1, with 41.7% exhibiting high expression. TMB-H and dMMR/MSI-H prevalence rates were 11.43% and 1.04%, respectively. TMB-H tended to be higher in PD-L1-low versus PD-L1-negative patients (P = 0.03). Mutations in PIK3CA and CASP8 were significantly higher in PD-L1-high versus -negative. PD-L1-high tumor microenvironment showed higher infiltration of Tregs, M1 macrophages, neutrophils, CD8 cells, and cancer-associated fibroblasts compared with PD-L1-low (q < 0.05). The expression of immuno-oncology (IO) markers, including IDO1, PDCD1, IFNG, CD274, HVACR2, CTLA4, LAG3, CD80, CD86, and PDCD1LG2, as well as T-cell inflammation and interferon-gamma scores, exhibited a concurrent decline in association with PD-L1 expression. The PD-L1-high group treated with ICIs had significantly longer TOT than the PD-L1-negative group (hazard ratio 0.758, 95% confidence interval 0.579-0.992, P = 0.044).

Conclusion: PD-L1-expressing ASCCs exhibit higher rates of PIK3CA and CASP8 mutations, increased IO markers, and higher inflammation. These tumors had longer treatment durations when treated with ICIs, suggesting that PD-L1 expression predicts treatment response.

Keywords: anal squamous-cell carcinoma; gastrointestinal cancer; immune checkpoint inhibitor; programmed death-ligand 1; tumor immune microenvironment; tumor mutation burden.

Copyright © 2025 The Author(s). Published by Elsevier Ltd.. All rights reserved.

背景： 肛门鳞状细胞癌（ASCC）是一种罕见的癌症。免疫检查点抑制剂（ICIs）被用作二线治疗。我们旨在分析ASCC的基因组和转录组谱，以预测ICI的有效性。

材料与方法： 进行了DNA和RNA的下一代测序（NGS）。通过免疫组织化学（IHC）测试程序性死亡配体1（PD-L1）表达为高（≥2+ 和 ≥5%）、低（1-2+ 和 ≥1%）和阴性（

结果： 在1242个肿瘤样本中，64.25%的样本表达PD-L1，其中41.7%表现出高表达。TMB-H和dMMR/MSI-H的发生率分别为11.43%和1.04%。与PD-L1阴性患者相比，PD-L1低表达患者的TMB-H更高（P = 0.03）。在PIK3CA和CASP8的突变中，在PD-L1高表达者比PD-L1阴性者显著较高。与PD-L1低表达相比，PD-L1高表达肿瘤微环境表现出更高的调节性T细胞、M1巨噬细胞、中性粒细胞、CD8+ T细胞和癌症相关成纤维细胞的浸润（q

结论： 表达PD-L1 的ASCC表现出更高的PIK3CA和CASP8突变率、增加的IO标志物以及更高的炎症。这些肿瘤在接受ICIs治疗时具有更长的治疗时间，这表明PD-L1 表达可以预测治疗反应。

关键词： 肛门鳞状细胞癌；胃肠道癌症；免疫检查点抑制剂；程序性死亡配体1；肿瘤免疫微环境；肿瘤突变负荷。