Description
Testicular choriocarcinoma is a highly aggressive, rare nonseminomatous germ cell tumour of the testis, characterised by the presence of trophoblastic cells. It may present as a pure form or more commonly as a component of mixed germ cell tumours. It is known for its rapid hematogenous spread and high human chorionic gonadotropin (hCG) production.
Pathogenesis
The pathogenesis of testicular choriocarcinoma is not completely understood. Like other germ cell tumours, it likely originates from primordial germ cells or gonocytes. The tumour comprises two main cell types: cytotrophoblasts and syncytiotrophoblasts. These cells are capable of producing hCG, a hormone normally produced during pregnancy.
Epidemiology, Risk Factors & Associations
- Testicular choriocarcinoma is rare, accounting for less than 1% of testicular germ cell tumours.
- It can be seen in teenagers and young adults, with a peak incidence between 15 and 30 years of age.
- Risk factors for testicular choriocarcinoma are similar to other testicular cancers and include cryptorchidism (undescended testicles), a history of testicular dysgenesis, and a family history of testicular cancer.
Clinical Features
- Presents with symptoms similar to other testicular cancers, such as a painless testicular mass or swelling.
- Due to its high hCG production, patients may experience symptoms related to this hormone, such as gynaecomastia (breast enlargement in males).
- Symptoms of metastasis may be the first sign of the disease given its aggressive nature. These could include back or abdominal pain, cough or shortness of breath, or neurological symptoms depending on the site of metastasis.
Complications
- Rapid haematogenous spread can lead to metastasis to various organs, particularly the lungs, liver, and brain.
- Metastases from choriocarcinoma are often haemorrhagic (helps differentiate it from other metastase). Choriocarcinoma cells have a propensity to invade blood vessels, leading to haemorrhagic metastases. Pulmonary metastases can cause haemoptysis and cerebral metastases can cause neurological symptoms.
- High hCG levels can lead to thyrotoxicosis due to the structural similarity of hCG to thyroid-stimulating hormone (TSH).
Pathological Features
Histopathology
- Tumour consists of biphasic population of cytotrophoblasts and syncytiotrophoblasts.
- Haemorrhage and necrosis are common findings.
Serology
- Elevated levels of serum hCG.
- Lactate dehydrogenase (LDH) may also be increased.
Radiological Features
General Features
- Testicular ultrasound usually shows a heterogeneous mass with areas of necrosis or haemorrhage.
US
- B-mode: The primary tumour generally appears as a heterogeneous, hypoechoic mass with irregular borders.
- Colour Doppler: Increased vascularity can often be noted due to hypervascular nature of the tumour.
- US of the scrotum: Often reveals a mass that is separate from the testis, frequently associated with hydrocele.
CT
- Non-contrast CT: Lesions often appear heterogeneous due to areas of necrosis, haemorrhage, and calcification.
- Post-contrast CT: Shows enhancement of the viable tumour areas, while necrotic areas remain non-enhancing.
- CT Chest/Abdomen/Pelvis: Can help identify metastases. Lung metastases may appear as multiple nodules with random distribution, often with areas of haemorrhage.
MRI
- MRI can be used for further characterisation of the primary tumour and detection of brain metastases.
- T1WI: The tumour shows heterogeneous signal intensity with high-signal-intensity areas representing haemorrhage.
- T2WI: The tumour appears as a mixed-intensity mass due to haemorrhage and necrosis.
- Post-contrast: There is enhancement in the viable areas of the tumour.
Diagnosis
- The diagnosis is typically made by a combination of clinical examination, elevated hCG levels, and characteristic histological findings on testicular biopsy or orchiectomy specimen.
- Imaging is used to detect metastasis.
Differential Diagnosis
- Testicular Seminoma: Typically presents in younger men and often manifests as a painless testicular mass. Unlike choriocarcinoma, seminomas tend to be hypovascular, show homogeneous enhancement on imaging, and beta-hCG is usually only slightly elevated or normal.
- Testicular Embryonal Carcinoma: This can present similarly to choriocarcinoma but tends to occur in younger men. On imaging, they appear as heterogeneous masses, usually with a cystic component. They can elevate both AFP and beta-hCG levels but not typically to the high levels seen in choriocarcinoma.
- Testicular Yolk Sac Tumour: These tumours primarily affect children under 3 years of age. Yolk sac tumours often show mixed echogenicity on ultrasound and can have areas of haemorrhage or necrosis. They are associated with elevated AFP levels, unlike choriocarcinoma.
- Testicular Teratoma: Teratomas may contain various tissue types that can mimic the appearance of choriocarcinoma on imaging, but they often have characteristic calcifications. Teratomas in postpubertal men can be malignant but do not typically raise beta-hCG levels.
- Testicular Lymphoma: Most common in older men, often presents bilaterally and is associated with systemic symptoms. Imaging shows homogeneously hypoechoic masses. Serum tumour markers are typically normal.
Management
- Management typically involves radical inguinal orchiectomy for the primary tumour.
- Given its aggressive nature, adjuvant chemotherapy is generally required.
- Radiotherapy may be used for certain metastatic sites.
- Due to high hCG levels, thyroid function should be monitored and managed appropriately.