[Future perspective of radiation therapy for superficial esophageal cancer]

Superficial esophageal cancer (SEC) is defined as esophageal cancer limited to the submucosal layer, and includes mucosal and submucosal cancer. Based on the criteria of the Japanese Society for Esophageal Disease, mucosal and submucosal cancer are classified according to location: epithelial layer (m1); proper mucosal layer (m2); muscularis mucosa (m3); upper third of the submucosal level (sm1); middle third of the submucosal layer (sm2); and lower third of the submucosal level (sm3). Irrespective of the treatment method, the depth of invasion is one of the most important prognostic factors of SEC because lymph node metastasis markedly increases in lesions infiltrating the lamina muscularis mucosa (m3). The best management technique for small m1 and m2 esophageal cancers is generally endoscopic mucosal resection (EMR). For m3-sm3 SEC, extensive lymph node dissection has been the most widely used form of treatment. However, a recent study has shown that for m3 and sm1 cancer, EMR seems to be as effective as surgery. Therefore, EMR may become the standard therapy for m3 and sm1 cancer. The role of radiation therapy in the treatment of SEC has not been established, and radiation therapy has tended to be used for SEC patients who are not suitable for EMR or surgery. The treatment outcomes of radiation therapy are encouraging and seem to be comparable with those of other treatment modalities. Radiation therapy is a promising method for treating SEC and may become standard therapy for certain subgroups of SEC. However, many problems concerning radiation therapy, including optimal radiation dose, optimal radiation field, and the role of intracavitary irradiation, remain to be solved. Thus, standardization of radiotherapy is an urgent issue.