What is the fine-grained topic of the following text: Intensive research into risk factors combined with the ability to identify precursor lesions (e.g.squamous dysplasia in esophageal squamous cell carcinoma and Barrett's esophagus in esophageal adenocarcinoma) has paved the way for studies of chemoprevention for esophageal cancer, some of which have shown promising results. Only return the topic.
Chemoprevention studies for esophageal cancer