PULMONARY PLEOMORPHIC CARCINOMA WITH KRAS G12C MUTATION AND HIGH PD-L1 EXPRESSION: A CASE REPORT AND LITERATURE REVIEW

Pulmonary pleomorphic carcinoma (PPC) is a rare subtype of pulmonary sarcomatoid carcinoma (PSC) within the non-small cell lung cancer category, characterized by significant histological heterogeneity that complicates diagnosis. A 71-year-old male with a 55-pack-year smoking history and chronic obstructive pulmonary disease (COPD) presented with four months of progressive dyspnea, nonproductive cough, pleuritic chest pain, weight loss, and hemoptysis. Physical examination identified decreased breath sounds in the lower right lung field and hypoxemia. 
Contrast-enhanced computed tomography (CT) revealed a large (7.5 cm) mass in the lower right lobe with associated hilar lymphadenopathy. PET-CT demonstrated intense FDG uptake (SUVmax 18.5) without evidence of distant metastasis. CT-guided core biopsy revealed a high-grade neoplasm composed of pleomorphic spindle cells and multinucleated giant cells with necrosis. Immunohistochemical (IHC) analysis confirmed PSC, positive for cytokeratin (AE1/AE3), vimentin, and p40, and negative for TTF-1 and Napsin A. Next-generation sequencing identified a KRAS G12C mutation, high tumor mutational burden, and 60% PD-L1 expression. The patient underwent right lower lobectomy with nodal dissection, achieving R0 resection of stage IIIB disease, followed by adjuvant carboplatin-paclitaxel chemotherapy and mediastinal radiotherapy. 
At 12 months, surveillance CT identified bilateral pulmonary nodules confirmed as metastatic recurrence, prompting initiation of pembrolizumab. After six months, the disease progressed to involve the liver and bones, leading to death 22 months after diagnosis.