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

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.