Primary Pulmonary Hyalinizing Clear Cell Carcinoma: Diagnostic Challenges and Pathologic Features in a CT‐Guided Biopsy Case

Abstract Primary pulmonary hyalinizing clear cell carcinoma (HCCC) is a rare salivary gland‐type tumor; most of the cases reported in the literature were diagnosed by surgical resection specimens. Herein, we present a case of pulmonary HCCC diagnosed with computed CT‐guided percutaneous biopsy and discuss its clinicopathologic characteristics and diagnostic strategy. Microscopically, the lesion was mainly composed of small‐to‐medium‐sized epithelioid cells with eosinophilic or transparent cytoplasm in a background of hyalinized fibrosis. The tumor cells showed immunoreactivity for CK and p63. The Ki67 proliferative index was 1%–5%, while TTF‐1, CgA, S100, Syn, Desmin, SMA and PD‐L1 staining were all negative. EWSR1 rearrangement was identified by break‐apart fluorescence. The report highlights a case of pulmonary HCCC with negative PD‐L1. The combination of tumor location, immunophenotypes and genetic alterations would be harnessed to differentiate HCCC from other tumors.