Hyalinizing clear cell carcinoma of the left main bronchus diagnosed with Ewing sarcoma breakpoint region 1::activating transcription factor 1 fusion: A case report

Rationale: Hyalinizing clear cell carcinoma (HCCC) of the bronchus is extremely rare. In addition, its rarity makes an accurate histological diagnosis difficult. Herein, we report a case of HCCC in the left main bronchus diagnosed by the detection of Ewing sarcoma breakpoint region 1::activating transcription factor 1 (EWSR1::ATF1 ) fusion transcript using reverse transcription-polymerase chain reaction (RT-PCR). Patient concerns: A 56-year-old woman presented with a tumor obstructing the left main bronchus on physical examination computed tomography. A bronchoscopic biopsy confirmed a malignant tumor but did not provide a definitive diagnosis. Interventions: Sleeve resection of the left main bronchus was performed. The intraoperative frozen section was negative for cancer in both the proximal and distal bronchial stumps. Diagnosis: General immunohistochemical staining was performed, and mucoepidermoid carcinoma and HCCC were suspected. RT-PCR revealed positive results for EWSR1::ATF1 fusion transcript, and the tumor was finally diagnosed as HCCC. Outcomes: The patient was discharged without any postoperative complications. Sixty-five months have passed since surgery, and no cancer recurrence has been observed. Lessons: Although hematoxylin and eosin staining and immunostaining alone were not sufficient to distinguish HCCC from mucoepidermoid carcinoma and other malignant tumors, adding genetic testing for EWSR1 rearrangement led to a definitive pathological diagnosis.