Collision tumor of the esophagus: report of a case with mixed squamous cell carcinoma and gastrointestinal stromal tumor.

Esophageal cancer is mainly divided into squamous cell carcinoma and adenocarcinoma. Epidemiologically, the former contributes to 90% of worldwide esophageal cancer cases, while adenocarcinoma contributes to two-thirds of cases in developed countries. Although other rare types and collision with multiple histological types of tumors do occur in the esophagus, it is very rare for a gastrointestinal stromal tumor (GIST) to collide with an epithelial malignant tumor. To date, only three cases have been reported in the literature. The current study reported a 69-year-old male patient with squamous cell carcinoma and GIST in the middle esophagus. There was no merging of tissue components between these tumors. This study together with a literature review indicates that esophageal collision tumors have been increasingly reported in recent years. Histology and immunohistochemistry are needed to make a differential diagnosis. The exact oncogenic mechanism or the interaction of two independent neoplasms still remains to be determined, and further investigation, such as electron microscopy and genetic analysis, may help to elucidate the pathogenesis of the colliding tumors.