A 38-year-old Indian male with no prior medical history presents with a mediastinal mass on chest X-ray. Serum β-human chorionic gonadotropin (β-hCG) is 5,200 mIU/mL and alpha-fetoprotein (AFP) is 890 ng/mL. Which investigation is most appropriate as the next step to confirm the diagnosis?

Explanation

## Diagnostic Approach to Mediastinal Mass with Elevated Germ Cell Tumor Markers **Clinical Context:** - Young male + mediastinal mass + markedly elevated β-hCG and AFP - This marker pattern is **pathognomonic for germ cell tumor (GCT)** - Differential: primary mediastinal GCT vs. metastatic testicular GCT **Why Biopsy is Correct:** - **Tissue diagnosis is mandatory** to confirm GCT and determine histology (seminoma vs. non-seminomatous) - Biopsy allows assessment of tumor type, which guides chemotherapy regimen selection - **Marker elevation alone cannot distinguish** between primary mediastinal GCT and metastatic testicular GCT - Histology determines prognosis and treatment intensity **Key Point:** While elevated β-hCG and AFP strongly suggest GCT, **histological confirmation is essential** because treatment differs significantly between seminoma (single-agent chemotherapy) and non-seminomatous GCT (multi-agent regimens). **High-Yield:** In mediastinal masses with GCT markers, biopsy takes precedence over other investigations to establish tissue diagnosis and guide therapy.