Hyalinizing Clear Cell Carcinoma of the Lung: Case Report and Review of the Literature.

OBJECTIVES: Hyalinizing clear cell carcinoma (HCCC) is common in head and neck sites but extremely rare in the lung. This case report describes an HCCC in the lung of a 54-year-old female patient. METHODS: We summarize the histomorphologic, immunophenotypic, and molecular features for our and three previously reported HCCCs of the lung with emphasis on potential diagnostic pitfalls. RESULTS: Sections of a well-circumscribed 3.5-cm lung mass were characterized by a bronchocentric tumor growing in sheets, nests, and cords in a background of hyalinized stroma. Tumor cell appearance was clear to eosinophilic, lacking significant pleomorphism or mitotic activity. By immunohistochemistry, the tumor cells were strongly positive with antibodies to pan-keratin, p63, and CK5/6 while negative for CK7, CK20, thyroid transcription factor 1, napsin A, chromogranin, and synaptophysin. Next-generation sequencing demonstrated an EWSR1-ATF1 fusion transcript. CONCLUSIONS: Awareness of key morphologic features of pulmonary HCCC is crucial for the recognition of this rare entity in the lung. Ancillary studies, including immunohistochemistry and molecular testing, are essential for the distinction from its mimics.