Esophageal squamous dysplasia.

Esophageal squamous dysplasia (ESD) appears to be the most important precursor for squamous cell carcinoma (SCC), and this observation is supported by early molecular findings. Pathologists in high incidence areas of the world, such as China, frequently may encounter ESD during surveillance cytology and biopsy screenings of high risk populations. ESD in low risk areas, such as the United States, is more commonly seen in esophagi resected for squamous cell carcinoma.