Uncovering PD-L1 among immune cell predictive biomarkers and actionable genetic alterations in anal squamous-cell carcinomas in the era of immunotherapy.

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.