Thymic tumour

Thymomas account for the vast majority of thymic neoplasms and are often associated with autoimmune or neurological syndromes, most commonly myasthenia gravis.

About one third of thymomas are asymptomatic and identified as an incidental radiographic finding. A chest computed tomography (CT) with intravenous contrast can be diagnostic.

Small, encapsulated tumours are resected for both pathological diagnosis and treatment. For anterior mediastinal tumours with a substantial chance of representing lymphoma, core needle biopsy is recommended. Positron emission tomography (PET)/CT scan can be very useful in differentiating thymoma from lymphoma without a biopsy (lymphoma has a far higher maximum standardised uptake value [SUVmax] than non-invasive thymoma).

Thymic malignancies that are locally advanced at presentation are usually treated with induction therapy (chemotherapy ± radiotherapy) followed by reassessment for surgery. Patients with myasthenia gravis should have myasthenic symptoms optimised before surgery.

Thymomas are relatively indolent tumours with high cure rates; however, all thymomas are considered malignant. Prognosis depends largely on completeness of resection, stage (Masaoka-Koga staging system and the 8th edition of the American Joint Committee on Cancer TNM staging system), and WHO histology. Thymic carcinomas and neuroendocrine tumours of the thymus (NETT) are generally more aggressive.

Treatment for locally advanced and metastatic tumours should involve a multidisciplinary team of medical oncologists, thoracic surgeons, radiation oncologists, pathologists, and radiologists who have experience and expertise in thymic malignancies.

Thymic tumours are rare, although they are the most common anterior mediastinal tumours in adults.[1]Engels EA, Pfeiffer RM. Malignant thymoma in the United States: demographic patterns in incidence and associations with subsequent malignancies. Int J Cancer. 2003 Jul 1;105(4):546-51. https://onlinelibrary.wiley.com/doi/full/10.1002/ijc.11099 http://www.ncbi.nlm.nih.gov/pubmed/12712448?tool=bestpractice.com [2]Girard N, Ruffini E, Marx A, et al. Thymic epithelial tumours: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2015;26(suppl 5):v40-v55. https://www.sciencedirect.com/science/article/pii/S0923753419471779 http://www.ncbi.nlm.nih.gov/pubmed/26314779?tool=bestpractice.com Thymomas account for the majority of thymic neoplasms. Although smaller tumours are typically asymptomatic and identified incidentally on imaging (unless associated with myasthenia gravis), large tumours can present with chest discomfort, cough, and/or dyspnoea, with or without myasthenia gravis symptoms.[3]Detterbeck FC. Clinical value of the WHO classification system of thymoma. Ann Thorac Surg. 2006;81:2328-2334. https://www.annalsthoracicsurgery.org/article/S0003-4975(05)02367-2/fulltext http://www.ncbi.nlm.nih.gov/pubmed/16731193?tool=bestpractice.com About one third of thymomas are diagnosed as an incidental finding.

In-depth management of myasthenia gravis is beyond the scope of this topic. See Myasthenia gravis.