[Clinicopathological features and molecular genetic changes of lung salivary gland-type clear cell carcinoma]

Objective: To investigate the clinicopathological features, immunophenotype, differential diagnosis, molecular genetic changes and prognosis of salivary gland-type clear cell carcinoma (CCC) of the lung. Methods: Eight cases of salivary gland-type CCC of the lung diagnosed at Fudan University Shanghai Cancer Center and Shanghai Pulmonary Hospital, China from March 2017 to December 2020 were retrieved and analyzed. The pathological sections of these cases were studied using immunohistochemical staining, fluorescence in situ hybridization (FISH), and RNA-seq fusion gene detection based on next generation sequencing technique. The patients were followed up and the relevant literature was reviewed. Results: The 8 patients included 3 males and 5 females, with age ranging from 43 to 64 years (average, 58 years). All patients underwent radical lobectomy and lymph node dissection, while only one had lymph node metastases. The eight patients were followed up for 6 to 45 months, and were all recurrence-free. Histopathologically, the tumor was mainly composed of eosinophilic and clear cells arranged in trabecular, ribbon and nest patterns. Hyalinization was often observed in the stroma around the nest. Immunohistochemical staining showed that 8/8 cases were positive for EMA and CK7; 5/8 cases were positive for p63 and p40; 4/8 cases were positive for SOX10; and the cases were all negative for S-100, SMA and calponin. EWSR1 gene fusion was detected in all cases by FISH. RNA-seq fusion gene was detected in 6 cases based on next generation sequencing. The EWSR1-ATF1 gene fusion was detected in 5 cases, among which one case also had the ATF1-SPTLC2 gene fusion. All 5 cases with EWSR1-ATF1 gene fusion showed that EWSR1 exon 12/13 fused with ATF1 exon 3. And EWSR1-CREM gene fusion was detected in one case. Conclusions: Salivary gland-type CCC of the lung is an extremely rare primary lung tumor arising from the bronchial mucosa. The diagnosis and differential diagnosis of this tumor depend on classic histomorphology, especially the auxiliary detection of EWSR1 fusion gene. The primary treatment choice of this tumor is complete surgical resection. Lymph node metastases may occur, but the overall prognosis is good.