Stage IVA EGFR L858R lung adenocarcinoma with malignant effusions and thrombosis

What happened, in summary

This 37-year-old man was diagnosed with left upper-lobe lung adenocarcinoma after malignant cells were found in pleural fluid during evaluation for pleural effusion. The disease was staged as T3N2M1a, Stage IVA, and he also had malignant pericardial effusion, confirmed by pericardial fluid analysis. Molecular testing showed an EGFR exon 21 L858R mutation. Immunohistochemistry supported lung adenocarcinoma, with Napsin A positivity, weak TTF-1 staining in the pericardial sample, p40 negativity, and a Ki-67 rate of about 10%. In October 2024, malignant pericardial effusion required pericardiocentesis with catheter drainage. He then received carboplatin plus pemetrexed every 21 days for 6 cycles and daily osimertinib as long-term EGFR-targeted therapy. His course was complicated by cancer-associated thrombosis. Ultrasound found thrombi in the popliteal, posterior tibial, peroneal, and right internal jugular veins, and he was treated with rivaroxaban. In December 2024, he returned with more than 3 days of left upper-abdominal pain, chest tightness, and myocardial discomfort. Examination showed tenderness in the left upper abdomen and palpable splenic enlargement. Imaging showed a filling defect in the splenic artery and non-enhancement of part of the spleen, consistent with splenic artery embolism and splenic infarction. D-dimer was markedly elevated during the thrombotic presentation and later normalized with anticoagulation. During that admission, he received cefuroxime prophylaxis and therapeutic enoxaparin, followed by long-term anticoagulation. After treatment, his abdominal pain markedly improved, the infarcted splenic area decreased in volume, and the infarction did not progress. As of May 2025, serial monitoring showed gradual regression of multi-site thromboembolic disease, no new thrombus formation, and ongoing outpatient follow-up with chest CT and vascular ultrasound surveillance.