A 35-year-old woman presents with progressive dyspnea, chest pain, and superior vena cava syndrome. Chest X-ray shows a large anterior mediastinal mass. CT chest reveals a heterogeneous mass with areas of low attenuation and calcification. Laboratory investigations show elevated LDH (1200 U/L), elevated β-hCG (450 mIU/mL), and normal α-fetoprotein. What is the most likely diagnosis?

Explanation

## Diagnosis: Non-Seminomatous Germ Cell Tumor (Mixed Type) ### Clinical Presentation **Key Point:** Anterior mediastinal masses in young adults with elevated tumor markers (β-hCG and/or α-fetoprotein) strongly suggest germ cell tumors. This patient presents with: - Age 35 years (germ cell tumors peak in 20–40 years) - Anterior mediastinal location (classic site for mediastinal germ cell tumors) - SVC syndrome from mass effect - Mixed tumor markers: elevated β-hCG (indicates choriocarcinoma component) with normal α-fetoprotein ### Differential Diagnosis of Anterior Mediastinal Masses | Feature | Seminoma | Non-Seminomatous GCT | Thymoma | Thymic Lymphoma | |---------|----------|----------------------|---------|------------------| | **Peak age** | 20–40 yrs | 20–40 yrs | 40–60 yrs | Variable | | **Tumor markers** | ↑LDH only (50%) | ↑β-hCG, ↑AFP, or both | Normal | Normal | | **β-hCG elevation** | Rare (<5%) | Common (40–60%) | No | No | | **Heterogeneity** | Homogeneous | Heterogeneous (mixed elements) | Homogeneous | Variable | | **Calcification** | Rare | Common | Common | Rare | ### Why Non-Seminomatous GCT (Mixed Type)? **High-Yield:** The combination of: 1. **Elevated β-hCG** — indicates trophoblastic (choriocarcinoma) differentiation, which is NEVER seen in pure seminoma 2. **Normal α-fetoprotein** — rules out yolk sac tumor as the sole component but does not exclude mixed histology 3. **Heterogeneous appearance with calcification** — typical of mixed germ cell tumors (teratoma + choriocarcinoma elements) 4. **LDH elevation** — non-specific but consistent with high tumor burden **Clinical Pearl:** Any mediastinal germ cell tumor with β-hCG elevation is non-seminomatous by definition. Mixed germ cell tumors (teratoma + choriocarcinoma + embryonal carcinoma) are more common than pure histologies in the mediastinum. ### Management Implications - Requires chemotherapy (BEP: bleomycin, etoposide, cisplatin) as first-line treatment - Prognosis depends on IGCCCG risk classification (this patient has intermediate/poor risk given elevated LDH and β-hCG) - Surgery reserved for residual masses after chemotherapy **Mnemonic: 4 A's of Anterior Mediastinal Masses** — Aortic aneurysm, Acute leukemia/lymphoma, Anterior thyroid, And germ cell tumors (plus thymoma, teratoma)