A Curious Case of Clear Cell Morphology in a Patient with Lung Cancer: Diagnostic Challenges.

An 82-year-old woman with COPD presented to the emergency department with cough, increasing sputum production, wheezing, and worsening shortness of breath for two weeks. On imaging studies, the patient was found to have a right upper lobe spiculated nodule and an endobronchial lesion with near total occlusion of the right lower lobe bronchus with sub-segmental atelectasis. Bronchoscopy with EBUS-TBNA of subcarinal and right hilar lymph nodes revealed lung cancer with clear cell phenotype. Given the predominance of clear cell morphology, the diagnosis of metastatic renal or ovarian cancer was entertained. However, there was no evidence of renal or ovarian lesions on the PET-CT scan, ruling out the possibility. Salivary gland type lung cancer (STLC), which is responsible for less than 1% of all lung cancer cases in adults, was also considered. The two distinct STLCs that may have similar morphologic appearances are hyalinizing clear cell carcinoma (HCCC) and mucoepidermoid carcinoma (MEC). The other type of tumour in the lung that demonstrates a clear cell phenotype is perivascular epithelioid cell neoplasms or PEComa, which are mesenchymal in origin. Immunohistochemical staining was strongly positive for p63, CK5/6, CK7, CK-LMW, and negative for TTF-1, Napsin A, p16, and CK20. Additional staining, including HMB-45, S-100, and mucicarmine, were also negative. Next-generation sequencing for the salivary gland fusion panel, including EWSR1-ATF1 fusion and EWSR1 gene rearrangement for HCCC and MAML2 gene rearrangements for MEC, was negative. She was diagnosed with non-small cell lung cancer favouring squamous cell carcinoma with clear cell phenotype, a rare entity.