Canis ISSN: 2398-2942


Contributor(s): Vetstream Ltd, Isabelle Desmas-Bazelle


  • Thymoma is an invasive, slow-growing tumor in anterior mediastinum.
  • Second most common cranial mediastinal tumor.
  • Often associated with paraneoplastic syndromes: myasthenia gravis Myasthenia gravis , megaesophagus (up to 40% of cases), polymyositis, erythema multiforme, lymphocytosis,  hypercalcemia Hypercalcemia: overview. May occur with other tumors (lymphoma Lymphoma , osteosarcoma Osteosarcoma: axial skeleton , adenocarcinoma Adenoma / adenocarcinoma ).
  • Diagnosis: radiography, ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), cytology, histopathology, other procedures, eg immunological tests for serum acetylcholine-receptor antibody, electromyography, electrocardiography, may be indicated.
  • Treatment: surgery, may be combined with radiotherapy.
  • Prognosis: guarded to poor.



  • Tumor of thymic epithelial cells.
  • The qualification of benign vs malignant is based on invasiveness of the tumor rather than histologic features.


  • Mass in anterior mediastinum → compression of airway.
  • It is thought that immunological abnormalities induced by the diseased thymus lead to the development of paraneoplastic syndromes.
  • Epithelial cells promote T-cell proliferation and differentiation in benign form.
  • Malignant neoplasia is locally invasive → hemorrhage into mediastinum.
  • Hypercalcemia results from excessive production of parathyroid hormone-related peptide (PTHrp).
  • Ectopic cervical thymic carcinoma has been reported.


  • Weeks to months.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Reeve E J, Mapletoft E K, Schiborra F, Maddox T W, Lamb C R et al (2019) Mediastinal lymphoma in dogs is homogeneous compared to thymic epithelial neoplasia and is more likely to envelop the cranial vena cava in CT images. Vet Radiol Ultrasound 1-8 PubMed.
  • Rick T, Kleiter M, Schwendenwein I, Ludewig E, Reifinger M et al (2019) Contrast-enhanced ultrasonography characteristics of intrathoracic mass lesions in 36 dogs and 24 cats. Vet Radiol Ultrasound 60, 56-64 PubMed.
  • Rohrer Bley C, Meier V, Schneider U (2018) Dosimetric benefit of adaptive radiotherapy in the neoadjuvant management of canine and feline thymoma-An exploratory case series. Vet Comp Oncol 16(3), 324-329 PubMed.
  • Vessieres F, Rasotto R, Peters I, Villiers E, Berlato D et al (2018) Assessment of Lymphoid Molecular Clonality in Canine Thymoma. J Comp Pathol 158, 66-70 PubMed.
  • Wiles V, Haddad J, Leibman N, Avery A C, Hughes K L (2018) Metastatic thymoma in the liver of a dog. J Vet Diagn Invest 30(5), 774-778 PubMed.
  • Moller C A, Bender H (2017) Pathology in Practice. Metastatic lymphocyte-rich thymoma in a dog. J Am Vet Med Assoc 250(4), 387-390 PubMed.
  • Burgess K E, DeRegis C J, Brown F S, Keating J H (2016) Histologic and immunohistochemical characterization of thymic epithelial tumours in the dog. Vet Comp Oncol 14(2), 113-121 PubMed.
  • Goto S, Murakami M, Kawabe M, Iwasaki R, Heishima K (2016) Hypofractionated radiation therapy in the treatment of canine thymoma: Retrospective study of eight cases. Vet Radiol Ultrasound 58, 613-620 PubMed.
  • Burton A G, Borjesson D L, Vernau W (2014) Thymoma-associated lymphocytosis in a dog. Vet Clin Pathol 43(4), 584-548 PubMed.
  • Patterson M M, Marolf A J (2014) Sonographic characteristics of thymoma compared with mediastinal lymphoma. J Am Anim Hosp Assoc 50(6), 409-413 PubMed.
  • Pintore L, Bertazzolo W, Bonfanti U, Gelain M E, Bottero E (2014) Cytological and histological correlation in diagnosing feline and canine mediastinal masses. J Small Anim Pract 55(1), 28-32 PubMed.
  • Robat C S, Cesario L, Gaeta R, Miller M, Schrempp D (2013) Clinical features, treatment options, and outcome in dogs with thymoma: 116 cases (1999-2010). J Am Vet Med Assoc 243(10), 1448-1454 PubMed.
  • Faisca P, Henriques J, Dias T M, Resende L, Mestrinho L (2011) Ectopic cervical thymic carcinoma in a dog. J Small Anim Pract 52(5),266-270 PubMed.
  • Tepper L C, Spiegel I B, Davis G J (2011) Diagnosis of erythema multiforme associated with thymoma in a dog and treated with thymectomy. J Am Anim Hosp Assoc 47(2), e19-25 PubMed.
  • Batlivala T P, Bacon N J, Avery A C, Barabas K, Gunn-Christie R G (2010) Paraneoplastic T cell lymphocytosis associated with a thymoma in a dog. J Small Anim Pract 51(9), 491-494 PubMed.
  • Mayhew P D, Friedberg J S (2008) Video-assisted thoracoscopic resection of noninvasive thymomas using one-lung ventilation in two dogs. Vet Surg 37(8), 756-762 PubMed.
  • Zitz J C, Birchard S J, Couto G C, Samii V F,Weisbrode S E et al (2008) Results of excision of thymoma in cats and dogs: 20 cases (1984–2005.) JAVMA 232(8) PubMed.
  • Lana S, Plaza S, Hampe K, Burnett R, Avery A C (2006) Diagnosis of mediastinal masses in dogs by flow cytometry. J Vet Intern Med 20(5), 1161-1165 PubMed.
  • Holsworth I G, Kyles A E, Bailiff N L, Hopper K, Long C (2004) Use of a jugular vein autograft for reconstruction of the cranial vena cava in a dog with invasive thymoma and cranial vena cava syndrome JAVMA 225(8) PubMed.
  • Smith A N, Wright J C, Brawner W R Jr, LaRue S M, Fineman L (2001) Radiation therapy in the treatment of canine and feline thymomas: a retrospective study (1985-1999). J Am Anim Hosp Assoc 37(5), 489-496 PubMed.
  • Wood S L, Rosenstein D S & Bebchuk T (2001) Myasthenia gravis and thymoma in a dog. Vet Rec 148 (18), 573-574 PubMed.
  • Day M J (1997) Review of thymic pathology in 30 cats and 36 dogs. JSAP 38 (9), 393-403 PubMed.
  • Meleo K A (1997) The role of radiotherapy in the treatment of lymphoma and thymoma. Vet Clin North Am Small Anim Pract 27 (1), 115-129 PubMed.
  • Atwater S W, Powers B E, Park R D, Straw R C Ogilvie G K & Withrow S J (1994) Thymoma in dogs: 23 cases (1989-1991). JAVMA 205 (7), 1007-1013 PubMed.
  • Klebanow E R (1992) Thymoma and acquired myasthenia gravis in the dog - case report and review of 13 additional cases. JAAHA 28 (1), 63-69 VetMedResource.

Other sources of information

  • De Mello Souza C H (2020) Thymoma. In: Withrow & MacEwen's Small Animal Clinical Oncology. 6th Edn. Vail D, Thamm D & Liptak J (eds). Saunders W B, Philadelphia pp 778-781.
  • Ogilvie G K & Moore A S (1995) Thymoma in dogs. In: Managing the veterinary cancer patient - a practice manual. Veterinary Learning Systems, Trenton N J pp 445-448.