Genome Doubling Shapes High-Grade Transformation and Novel EWSR1::LARP4 Fusion Shows SOX10 Immunostaining in Hyalinizing Clear Cell Carcinoma of Salivary Gland.

Hyalinizing clear cell carcinoma (HCCC) is a rare indolent malignant tumor of minor salivary gland origin with EWSR1::ATF1 rearrangement. Pathologically, the tumor cells possess a clear cytoplasm in a background of hyalinized stroma. Generally, the tumor cells are positive for p63 and p40 and negative for s100 and α-smooth muscle actin, suggesting that they differentiate into squamous epithelium and not into myoepithelium. In this study, we performed a detailed histopathological and genomic analysis of 6 cases of HCCC, including 2 atypical subtypes-a case of "high-grade transformation" and 1 "possessing a novel partner gene for EWSR1." We performed a sequential analysis of the primary and recurrent tumor by whole-exome sequencing, RNA sequencing, Sanger sequencing, and fluorescence in situ hybridization to investigate the effect of genomic changes on histopathology and clinical prognosis. A fusion gene involving the EWSR1 gene was detected in all cases. Five cases, including the "high-grade transformation," harbored a known EWSR1::ATF1 fusion gene; however, 1 case harbored a novel EWSR1::LARP4 fusion gene. This novel EWSR1::LARP4-fused HCCC has a SOX10-positive staining, which is different from the EWSR1::ATF1-fused HCCC. According to whole-exome sequencing and fluorescence in situ hybridization analysis, the "whole-genome doubling" and focal deletion involving CDKN2A, CDKN2B, and PTEN were detected in HCCC with "high-grade transformation." Conclusively, we identified a novel partner gene for EWSR1, LARP4, in indolent HCCC. Importantly, "high-grade transformation" and poor prognosis were caused by whole-genome doubling and subsequent genomic aberrations.

Full-coverage TP53 deep sequencing of recurrent head and neck squamous cell carcinoma facilitates prognostic assessment after recurrence.

OBJECTIVES: This study aims to evaluate whether the accumulation of TP53 mutations is associated with clinical outcome by comparing full-coverage TP53 deep sequencing of the initial and recurrent head and neck squamous cell carcinoma (HNSCC). MATERIALS AND METHODS: Medical records and surgical specimens of 400 patients with HNSCC surgically treated with curative intent, of which 95 patients developed local or locoregional recurrence, were reviewed. Of these patients, 63 were eligible for genomic analysis. Full-coverage TP53 deep sequencing of 126 paired initial and recurrent tumor samples was examined using next-generation sequencing (NGS). Temporal changes in the mutation status, molecular characterization, and clinical outcome were compared. Fisher's exact test, Kaplan-Meier method, log-rank test, and Cox regression models were used for statistical analysis. RESULTS: Of the recurrent tumors, 22% harbored accumulation of TP53 mutations, and 16% lost the original mutation. The accumulation of TP53 mutations was significantly more frequent in oral cancer than in pharyngeal or laryngeal cancer (33% vs. 7%, p = 0.016). Two-year post-recurrence survival (PRS) was associated with TP53 status for recurrent tumors, but not for initial tumors. The TP53 status for recurrent tumors was an independent risk factor in multivariate analysis (hazard ratio, 5.76; 95% confidence interval, 1.86-17.8; p = 0.0023). CONCLUSION: Approximately one-third of the recurrent HNSCC cases showed a different TP53 status from the initial tumor. Temporal changes in the mutation status differed by primary site. Full-coverage TP53 deep sequencing of recurrent tumors was useful in predicting post-recurrence prognosis.