CRA41 CLEAR CELL STROMAL TUMOUR OF THE LUNG: FIRST REPORTED CASE IN MALAYSIA

Peter Natarajan¹, Ng Khai Lip¹, Nur Husna Mohd Aminudin¹, Ad Rian Chong¹, Kasuma Mohamed Nordin¹, Maryam Ahmad¹, Mohd Azali Bin Zakariah²

¹Hospital Melaka, Melaka, Malaysia
² Hospital Sultanah Aminah, Johor Bahru, Malaysia

Introduction
Clear cell stromal tumour (CCST) of the lung is an exceptionally rare primary pulmonary neoplasm, with only 19 cases reported worldwide as of July 2024. Its diagnosis is often challenging due to its rarity and nonspecific radiological and clinical features. This case highlights the first documented occurrence of CCST in Malaysia and emphasizes the role of immunohistochemistry (IHC) in diagnosis.

Case Report
A 37-year-old Chinese female with underlying right eye blindness, type 2 diabetes mellitus, and a 20 pack-year smoking history was found to have an incidental right upper lobe mass on routine chest radiography. Workup for pulmonary tuberculosis and tumour markers were unremarkable. Serial CT thorax imaging between December 2023 and July 2024 demonstrated a stable solitary right upper lobe nodule measuring approximately 3.0 × 3.9 × 3.1 cm. Bronchoscopy revealed an endoluminal mass occluding the RB1 bronchus. Biopsy showed a spindle cell neoplasm with clear cytoplasm. IHC demonstrated positivity for TFE3 and YAP1 C-terminus, with a Ki-67 index of <5%, supporting the diagnosis of CCST.

Discussion
This case represents the first report of pulmonary CCST in Malaysia. CCST is characterized by a recurrent YAP1::TFE3 gene fusion. In settings where molecular testing is unavailable, dual IHC positivity for TFE3 and YAP1 C-terminus can provide a useful surrogate marker, enhancing diagnostic specificity. Due to its rarity, CCST may be misdiagnosed as other clear cell neoplasms or sarcomatoid lesions.

Conclusion
The patient underwent right VATS and upper lobectomy, recovering well postoperatively. Histopathology confirmed the diagnosis with identical IHC findings. CCST is an emerging diagnostic entity. Awareness of its clinical and immunohistochemical profile is essential to guide accurate diagnosis and appropriate surgical management.