Thymoma vs Thymic Carcinoma: Key Differences Explained

Thymoma is the most common type of thymic tumour. It typically grows slowly and often remains confined to the thymus or nearby structures for a long period of time.

Many thymomas are diagnosed incidentally during imaging performed for other reasons. They are frequently associated with autoimmune conditions, particularly myasthenia gravis, as well as other immune-mediated disorders.

Pathologically, thymomas are classified into subtypes (A, AB, B1, B2, B3), which reflect their cellular appearance and help guide prognosis and management.

Thymic carcinoma is much rarer and biologically more aggressive than thymoma. Unlike thymoma, thymic carcinoma tends to invade surrounding tissues early and has a higher likelihood of spreading to lymph nodes or distant organs.

These tumours resemble carcinomas seen in other organs and often lack the organ-specific features seen in thymoma. As a result, thymic carcinoma is usually diagnosed at a more advanced stage and requires a more intensive treatment approach.

Although both arise from the thymus, the two conditions differ in several important ways:

Growth behaviour
Thymomas usually grow slowly, whereas thymic carcinomas tend to grow more rapidly and aggressively.

Invasiveness
Thymoma often remains localised, while thymic carcinoma commonly invades adjacent structures and spreads beyond the thymus.

Association with autoimmune disease
Thymoma is frequently associated with autoimmune conditions, particularly myasthenia gravis. This association is rare in thymic carcinoma.

Overall outcomes are more favourable in thymoma, especially when diagnosed early. Thymic carcinoma generally carries a poorer prognosis due to its aggressive nature.

Symptoms vary depending on tumour size, location, and stage. Some patients may have no symptoms at all, while others experience:

• Chest discomfort or pain
• Shortness of breath
• Persistent cough
• Difficulty swallowing
• Fatigue
• Symptoms related to myasthenia gravis, such as muscle weakness or drooping eyelids

Because these symptoms are non-specific, thymic tumours are often detected during imaging performed for other reasons.

Diagnosis typically begins with imaging, most commonly a CT scan of the chest, which can identify an anterior mediastinal mass. Further evaluation may include MRI or PET-CT to assess local invasion or spread.

A tissue diagnosis is usually required to distinguish thymoma from thymic carcinoma. This may be obtained through biopsy or surgical resection, depending on the clinical scenario.

Accurate pathological assessment is essential, as treatment strategies differ significantly between the two conditions.

Thymic tumours are staged using systems that assess:

• Tumour invasion into surrounding tissues
• Lymph node involvement
• Presence of distant metastases

Early-stage thymomas may be completely resectable, whereas thymic carcinomas are more likely to present at advanced stages.

Staging helps guide decisions regarding surgery, radiotherapy, and systemic treatment.

Treatment depends on tumour type, stage, and patient-specific factors.

Thymoma
Surgery is the cornerstone of treatment whenever feasible. Complete surgical removal offers excellent long-term control in early-stage disease. Radiotherapy or systemic therapy may be considered in selected cases.

Thymic carcinoma
Management often requires a multimodal approach, combining surgery (where possible), chemotherapy, and radiotherapy. Systemic treatment plays a larger role due to the higher risk of spread.

Treatment planning is best managed by a multidisciplinary thoracic oncology team.

Prognosis varies widely based on tumour type and stage at diagnosis.

Patients with early-stage thymoma often have excellent long-term outcomes following complete resection. In contrast, thymic carcinoma has a higher risk of recurrence and progression, even with aggressive treatment.

Ongoing follow-up is important for both conditions, as late recurrences can occur.