Thymic Carcinoma

Thymic carcinoma (TC) is a type of thymic epithelial neoplasm (see this term) characterized by a high malignant potential.

Epidemiology

The exact prevalence or incidence is unknown. It represents 1% of the anterior mediastinal tumors and occurs in all ages but more frequently between the ages of 30 and 60 years. The male to female ratio is 1.5:1.

Clinical description

Patients can be asymptomatic but more often present with chest-related symptoms (cough, chest pain), phrenic nerve palsy, or superior vena cava syndrome. Contrary to patients with thymoma (see this term), myasthenia gravis or paraneoplastic syndromes are rarely observed.

Etiology

Etiology is unknown.

Diagnostic methods

Diagnosis is based on clinical findings and on radiological studies. Chest X-rays reveals a mediastinal mass. Computed tomography, magnetic resonance imaging (MRI), magnetic resonance angiography (angio-MRI) and/or positron emission tomography (PET) further evaluate the lesion. Tissue biopsy, usually performed by CT- or ultrasound-guided percutaneous needle-biopsy, is used to confirm a diagnosis of malignancy. Complete excision is required for definitive histologic typing. TC is composed of atypical cells of an invasive nature and lacks immature (or cortical) T cells. Several histologic subtypes are observed: the most common are squamous cell carcinoma, mucoepidermoid carcinoma and lymphoepithelioma-like carcinoma while rarer variants include clear cell carcinoma, basaloid carcinoma, spindle cell carcinoma, and anaplastic carcinoma. Extremely rare variants include papillary carcinoma, adenocarcinoma, and rhabdoid carcinoma. The diagnosis of thymic carcinoma is one of exclusion, as there are no morphologic, immunohistochemical, ultrastructural or cytogenetic/molecular features that are pathognomonic for this tumor. Histologically, the tumors may resemble carcinomas commonly arising in other organs. For this reason, the diagnosis can only be established by exclusion through careful demonstration on clinical history, clinical examination, and radiographic and endoscopic examination of the absence of a primary tumor elsewhere.

Differential diagnosis

Differential diagnoses include lymphoma, germ-cell tumors (see these terms), and other primary thymic malignancies and metastatic cancers.

Management and treatment

Treatment consists in total thymectomy and complete tumor excision usually accompanied by neoadjuvant or adjuvant therapy consisting of radiotherapy, chemotherapy, or both. In case of metastatic TC, platinum-based chemotherapy is the first-line treatment.

Prognosis

Prognosis is poor due to the high frequency of recurrences and metastases in the pleura, lung, lymph nodes, bone, brain, and liver. The survival rate at 5 years is 35%.