Molecular pathology and potential therapeutic targets in esophageal basaloid squamous cell carcinoma

Basaloid squamous cell carcinoma (BSCC) is a rare and poorly differentiated variant of typical squamous cell carcinoma. Emerging studies show that genetic alterations are more frequent in BSCC than in conventional SCC, and some of which led to the identification of potential therapeutic targets in esophageal BSCC. Approximately half of the esophageal BSCC cases harbor either an EGFR mutation or amplification, and these occur in a mutually exclusive fashion. Therefore, the application of tyrosine kinase inhibitors may be beneficial to esophageal BSCC patients. This tumor is partly characterized by the activation of the Wnt and Hedgehog (HH) signaling pathways. Wnt signaling is activated by SFRP2 promoter hypermethylation and HH signaling is activated by the frequent mutations in PTCH1. Increasing evidence shows that the Wnt signaling pathway is involved in cross-talk with other developmental pathways, including the HH pathway. Therefore, pharmaceutical therapy targeting both the HH and Wnt pathways would be quite effective in patients with esophageal BSCC with highly malignant potential. In this review, we discuss the pathology, prognostic factors, genetic alterations and potential therapeutic targets in BSCC of esophagus.