Case Report: Complete endoscopic submucosal dissection for occult superficial esophageal squamous cell carcinoma concealed by a large esophageal leiomyoma.

Introduction: Benign-appearing gastrointestinal lesions may occasionally conceal malignancy and pose a diagnostic challenge. Esophageal leiomyomas are benign neoplasms; however, careful mucosal assessment remains essential to avoid missed diagnoses. Case description: We report the case of a 53-year-old asymptomatic woman in whom a large esophageal leiomyoma masked a superficial esophageal squamous cell carcinoma (ESCC). Subtle mucosal irregularity detected on endoscopy prompted further evaluation with narrow-band imaging and targeted biopsies, confirming carcinoma Conclusion: En bloc resection was achieved without complications. Histopathology confirmed a well-differentiated superficial ESCC with submucosal invasion (>200 μm, pT1b), negative horizontal and vertical margins, and no lymphovascular invasion. After postoperative pathology review, additional surgical treatment was recommended because of the risk associated with submucosal invasion; however, the patient strongly declined surgery. Contrast-enhanced CT showed no evidence of regional lymph node metastasis, and the patient subsequently underwent radiotherapy at a local hospital. At 2-year follow-up, endoscopic re-examination showed no recurrence, and the leiomyoma remained stable in size. This case underscores the importance of careful evaluation for occult malignancy hidden behind benign-appearing lesions and demonstrates that favorable outcomes can be achieved through individualized, multidisciplinary management, including endoscopic resection, adjuvant therapy, and close surveillance.