Persistent D-dimer Elevation in a Yolk Sac Germ Cell Tumor Without Thrombosis: A Potential Surrogate Marker of Tumor Necrosis

D-dimer is a widely used biomarker for thromboembolic events, but its role in oncology beyond clot detection remains underexplored. While transient elevation is common in cancer patients, persistent elevation without evidence of thrombosis is less well understood, particularly in germ cell tumors. We report the case of a 32-year-old male patient with a large anterior mediastinal yolk sac tumor who developed persistently elevated D-dimer levels despite multiple negative investigations for thrombosis, including CT pulmonary angiogram, ventilation-perfusion scan, and Doppler ultrasonography. Following debulking surgery, the patient showed clinical improvement and normalization of tumor markers, but D-dimer levels remained elevated at 2.4-2.5 mg/L. This case raises the possibility that persistent D-dimer elevation may reflect tumor necrosis or ongoing vascular remodeling rather than thrombosis or infection. If recognized, such a pattern could help clinicians avoid unnecessary anticoagulation and provide an adjunctive marker for residual tumor activity. D-dimer may have potential as a surrogate indicator of tumor dynamics in selected oncology settings. Further research is warranted to validate its prognostic or monitoring value in germ cell tumors.