The patient was a 66-year-old man who was admitted to Beijing Friendship Hospital mainly because of retrosternal pain during swallowing for more than six months. The main symptom was a stabbing pain in the chest behind the breastbone when swallowing solid food, which was relieved after swallowing. He did not report dysphagia, acid regurgitation, heartburn, nausea, vomiting, or melena. There was no significant change in body weight in the past six months. In terms of past history, the patient had a smoking history of more than 30 years, approximately 30 cigarettes per day, and had quit smoking for 4 years. The patient had no other underlying diseases and no family history of cancer. Physical examination revealed no obvious abnormality.
The patient underwent electronic endoscopy in a local hospital on February 22, 2022. Flaky erosions were observed 29 cm away from the incisors, and they were approximately 0.8*1 cm in size with surfaces covered with white hair. A biopsy was taken from the erosion site, and the local hospital's pathology suggested high-grade squamous intraepithelial neoplasia.
After admission, the patient's routine blood, liver and kidney function, electrolytes, myocardial enzymes and other laboratory tests showed no abnormalities. Only the tumor marker prostate-specific antigen was increased. Enhanced chest computed tomography showed no esophageal space-occupying lesions or swollen lymph nodes around the esophagus.
The patient underwent endoscopy in our hospital on March 29, 2022. A type 0-IIa lesion, approximately 1*1 cm in size, was located in the middle of the esophagus and 28-29 cm from the incisors ( Figure 1A ). The lesion mucosa was red and rough, with good extension. The lesion boundary was clear under white light observation, and the lesion mucosa did not stain with 1.25% iodine staining. Blue laser imaging magnifying endoscopy (BLI-ME) revealed positive background staining ( Figures 1B, C ). The Japan esophageal society (JES) type was B1, and the avascular area (AVA) type was small AVA. Endoscopic ultrasonography suggested that the five-layer structure of the esophageal wall at the lesion was clear, and the mucosal layer was slightly thickened ( Figure 1D ). ESD was performed to remove the diseased mucosa, and 18*14-mm esophageal mucosal tissue was obtained ( Figures 1E, F ). There were no short-term complications, such as bleeding, perforation or infection, after endoscopic surgery.
The postoperative pathological results showed that there were two malignant tumor components in the tissue submitted for examination ( Figures 2 ,  3A ). And microscopy revealed an abrupt transition between these two components that developed adjacently but never intermingled ( Figure 3B ). Combined with preoperative evaluation that failed to confirm any primary lesions that had metastasized to the esophagus, this patient was unequivocally diagnosed with an esophageal collision tumor. One of them was SqCC (approximately 4*2 cm in area) ( Figure 3C ). The cancer tissue infiltrated the lamina propria (pT1a-LPM). Another cancerous tissue was tubular and had cribriform structures with variably solid components ( Figure 3D ), which was located in the lamina propria and submucosa, with an infiltration depth of 60 mum into the submucosa (pT1b-SM1). Subsequent immunohistochemistry of this component yielded positive CD 117, S-100, p63, and CK8 staining ( Figures 3E, F ). Using the World Health Organization's classification of tumors of the digestive system 2019, we diagnosed this component as an AdCC (14*4 mm in area). The horizontal resection margin was clean, and the tumor was approximately 20 microns away from the nearest vertical resection margin. This lesion was free of lymphovascular invasion.
Since the lesion had clean incisors and no vascular infiltration, additional surgery or chemoradiotherapy was not considered. After 6 months of follow-up, the patient did not complain of any discomfort. Three months after surgery, endoscopy revealed that there was a white scar approximately 28 to 29 cm away from the incisors in the middle esophagus, and esophageal stenosis and esophageal fistula were not observed. No abnormality was observed by narrowband light imaging (NBI), and no light staining was found after staining with 1.25% iodine solution.