Clinicopathological and mutational analysis of esophageal basaloid squamous cell carcinoma

Esophageal basaloid squamous cell carcinoma (EBSCC) is a poorly differentiated variant of esophageal squamous cell carcinoma (ESCC). We aimed to investigate the clinicopathological and molecular biological characteristics of EBSCC and enrolled 58 patients with EBSCCs. Clinicopathological factors including age, sex, tumor size and location, gross tumor type (superficial, protrusive, ulcerative, and unclassifiable), lymphovascular invasion, infiltrative growth, intramural invasion, TNM stage, and dominant histological type were examined. EBSCCs were classified into four types (solid, cribri, microcystic, and tubular) according to the dominant histology. Next-generation sequencing (NGS) of a cancer hotspot panel was performed in 19 cases. NGS identified TP53 as the most frequently mutated gene, and copy number variation analysis revealed the most frequent loss of heterozygosity (LOH) at the ataxia telangiectasia mutated (ATM) and retinoblastoma 1 (RB1) loci. Target sequencing for TP53 was performed for the remaining 39 cases. We also performed LOH analysis for TP53, ATM, and RB1 and immunohistochemical staining for p53, ATM, and Rb in all cases. The rates of TP53 mutations and LOH and p53 aberrant expression were high (79.3%, 63.2%, and 72.4%, respectively); however, the frequencies were similar to those reported for ESCC. LOH rates of the RB1 and ATM loci were also high (55.3% and 67.2%, respectively). Overall survival rate was 66.5%, and recurrence-free survival rate was 55.0%. Only conventional clinicopathological factors had a prognostic impact in EBSCC; the microcystic type had the poorest prognosis. Our findings could be useful in developing novel treatment strategies for EBSCC.