Primary pulmonary hyalinising clear cell carcinoma: Two cases and literature review

Hyalinising clear cell carcinoma (HCCC) of the lung is an extremely rare tumour that is just recently recognised as one of the salivary gland-type tumours (SGTT) in the latest WHO classification of thoracic tumours. Eleven cases have been reported in English literature since Joaquín et al. reported the first case. Given the very limited number of cases, the clinical and histological features of pulmonary HCCC are equivocal. Herein, we present two cases of pulmonary HCCC. The patients were a 66-year-old man and a 48-year-old woman. The mass was located on the right main bronchus and right middle lobar bronchus separately. One was 2 cm and the other was 3.3 cm in the greatest dimension. The tumours were comprised of small monomorphic cells with clear or eosinophilic cytoplasm and infiltrated in a hyalinising stroma arranged in nests, cords, sheets and trabeculae. Their morphology resembled their head and neck counterparts. Immunohistochemically, the tumour cells were positive for AE1/AE3, P63, while negative for TTF1, Calponin, S-100, HMB45 and PAX8. Ki-67 labeling ranges from 3% to 10%. Fluorescence in situ hybridisation (FISH) demonstrated EWSR1 rearrangement and Next-generation sequencing (NGS) demonstrated EWSR1- ATF1 (exon 11: exon 3) fusion in case one and EWSR1- ATF1 (exon 2: exon 12) fusion in case two. This is the first time to report the EWSR1-ATF1fusion point other than exon 11: exon 3 in pulmonary HCCC. Case one recurred two years after local resection but didn't metastasise during follow-up 36 months. Case two is alive without disease after lobectomy during follow-up 14 months.