Germ Cell Tumours of the Mediastinum
Seminoma vs NSGCT, tumour markers, mature teratoma, and the AFP rule.
Overview
Mediastinal germ cell tumours (GCTs) arise from pluripotent germ cells or embryonal cells. They are also known as extra-gonadal GCTs. About 5–10% of all GCTs arise in the mediastinum; 95% are found in the anterior mediastinum (prevascular compartment). They occur most commonly between ages 20–40, with equal sex distribution — except mediastinal seminoma, which is almost exclusively found in males. In males, seminoma is commonly associated with Klinefelter's syndrome.
Mediastinal GCTs are benign in approximately 80% of patients (mature teratoma and dermoid cyst). Malignant GCTs carry a worse prognosis than their gonadal counterparts.
Always examine the testes and obtain scrotal ultrasound in any young male with an anterior mediastinal mass — mediastinal GCT must be distinguished from a gonadal primary with mediastinal metastasis, as this changes staging, prognosis, and treatment significantly.
Classification
| Category | Tumour types |
|---|---|
| Seminomatous GCT | |
| Seminoma · Germinoma | |
| Non-seminomatous GCT (NSGCT) | |
| Benign | Mature teratoma · Dermoid cyst |
| Malignant | Embryonal carcinoma · Choriocarcinoma · Immature (malignant) teratoma · Yolk sac tumour |
Tumour markers
| Marker | Seminoma | NSGCT |
|---|---|---|
| AFP (alpha-fetoprotein) | Normal — raised AFP excludes pure seminoma | Raised in 80% (yolk sac, embryonal) |
| β-hCG | Raised in 10% | Raised in 30–35% (choriocarcinoma) |
| PLAP (placental alkaline phosphatase) | Raised in 50% | Normal |
| LDH | Raised | Raised |
A raised AFP in any mediastinal anterior mass in a young male = NSGCT or mixed GCT until proven otherwise. Pure seminoma never raises AFP. This distinction has direct therapeutic implications — seminoma is radiosensitive, NSGCT is not.
Seminoma vs NSGCT — key differences
| Feature | Seminoma | NSGCT |
|---|---|---|
| AFP / β-hCG | Rarely raised | Raised in ~90% |
| Associated syndromes | None | Klinefelter's, trisomy 8, 5q deletion |
| Radiosensitivity | High | Insensitive |
| Metastatic behaviour | Remain intrathoracic | Frequently disseminated |
| Primary treatment | Radiation ± cisplatin chemotherapy | Cisplatin-based combination chemotherapy |
| Remission rate | >80% | CR in 55–60%, PR in 30–35% |
| 5-year survival | 50–80% | 50–60% |
Mature teratoma (dermoid cyst)
The most common mediastinal GCT. Contains well-differentiated elements from all three germ layers — ectoderm (skin, hair, teeth — giving it the 'dermoid' appearance), mesoderm (muscle, cartilage, bone), and endoderm (gut, respiratory epithelium). The classic CT finding is a cystic mass with fat attenuation and calcification in the anterior mediastinum.
Treatment: Complete surgical excision is curative. VATS or sternotomy depending on size. Rupture into bronchus causes expectoration of hair and sebum (trichoptysis). Malignant transformation to immature teratoma or carcinosarcoma is rare but documented.
Treatment overview
- Mature teratoma: complete surgical excision — curative
- Seminoma: cisplatin-based chemotherapy ± radiotherapy; surgery for residual mass after chemotherapy
- NSGCT: cisplatin-based combination chemotherapy (BEP — bleomycin, etoposide, cisplatin); surgery for residual masses after chemotherapy
For current BEP regimens, salvage chemotherapy protocols, and management of residual masses after chemotherapy, refer to ESMO testicular cancer guidelines (extragonadal GCTs follow similar protocols).
All clinical content should be verified against current guidelines before clinical application. This resource is intended for revision and educational purposes only.
Standard textbooks
- Shields TW, LoCicero J, Reed CE, Feins RH. General Thoracic Surgery. 7th ed. Lippincott Williams & Wilkins.
- Sellke FW, del Nido PJ, Swanson SJ. Sabiston & Spencer Surgery of the Chest. 9th ed. Elsevier.
- Pearson FG, et al. Thoracic Surgery. 3rd ed. Churchill Livingstone.