Felis ISSN 2398-2950

Thymus: neoplasia

Contributor(s): Laura Garrett, Isabelle Desmas-Bazelle


  • Old cat - tumor is most likely to be thymoma (rare); paraneoplastic syndromes may be present.
  • Young cat - most likely to be anterior mediastinal (thymic) lymphosarcoma, although thymoma may occur.
  • Other thymic masses: thymic hyperplasia, thymic branchial cyst formation, thymic hemorrhage, thymic amyloidosis, other very rare neoplasms.
  • Signs: tachypnea, dyspnea due to pleural effusion and mediastinal mass, cranial vena cava syndrome (edema head, neck, forelimbs), paraneoplastic syndromes (rare), anorexia, regurgitation, dysphagia, drooling.
  • Diagnosis: radiography, ultrasonography, CT scan, cytology, histopathology, flow cytometry, PCR for antigen rearrangement.
  • Treatment: surgery, may be combined with radiotherapy, chemotherapy.
  • Prognosis: good, particularly if tumor is encapsulated; metastases very rare if thymoma, depends on response to chemotherapy for lymphoma.



  • Thymoma - FeLV Feline leukemia virus disease not involved.
  • Historically most (>80-85%) mediastinal lymphosarcoma cases were associated with feline leukemia virus which can cause malignant transformation of lymphocytes. This is no longer the case following widespread FeLV vaccination.


  • Mass in anterior mediastinum  →  pleural effusion, respiratory compromise.
  • It is thought that immunological abnormalities induced by the diseased thymus lead to the development of paraneoplastic syndromes.


  • Weeks although may present acutely.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Fournier Q, Bavcar S, Philbey A W, Smith S, Varjonen K (2019) A previously undescribed cutaneous paraneoplastic syndrome in a cat with thymoma. Vet Dermatol 30(4), 342-e98 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.
  • Spugnini E P, Menicagli F, Pettorali M, Baldi A (2017) Ultrasound guided electrochemotherapy for the treatment of a clear cell thymoma in a cat. Open Veterinary Journal 7(1), 57-60 PubMed.
  • Griffin M A, Sutton J S, Hunt G B, Pypendop B H, Mayhew P D (2016) Video-Assisted Thoracoscopic Resection of a Noninvasive Thymoma in a Cat with Myasthenia Gravis Using Low-Pressure Carbon Dioxide Insufflation. Vet Surg 45(S1), O28-O33 PubMed.
  • Nagata N, Miyoshi, Otake Y, Suzuki H, Kagawa Y et al (2016) Temporal deterioration of neurological symptoms and increase of serum acetylcholine receptor antibody levels after thymectomy: a case report of a cat with myasthenia gravis. J Vet Med Sci 78(12), 1893-1896 PubMed.
  • Fabrizio F, Calam A E, Dobson J M et al (2014) Feline mediastinal lymphoma: a retrospective study of signalment, retroviral status, response to chemotherapy and prognostic indicators. J Feline Med Surg 16(8), 637-644 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.
  • Sato H, Fujino Y, Chino J, Takahashi M, Fukushima K et al (2014) Prognostic Analyses on Anatomical and Morphological Classification of Feline Lymphoma. J Vet Med Sci 76(6), 807-811 PubMed.
  • Hill P B, Brain P, Collins D, Fearnside S, Olivry T (2013) Putative paraneoplastic pemphigus and myasthenia gravis in a cat with a lymphocytic thymoma. Vet Dermatol 24(6), 646-649 PubMed.
  • Singh A, Boston S E, Poma R (2010) Thymoma-associated exfoliative dermatitis with post-thymectomy myasthenia gravis in a cat. Can Vet J 51(7), 757-760 PubMed.
  • Fujino Y, Liao C-P, Zhao Y S,  Pan J, Mathes L E (2009) Identification of a novel common proviral integration site, flit-1, in feline leukemia virus induced thymic lymphoma. Virology 386 16-22 PubMed.
  • Lara-Garcia A, Wellman M, Burkhard M J, Machado-Parrula C, Valli V E et al (2008) Cervical thymoma originating in ectopic thymic tissue in a cat. Vet Clin Pathol 37(4), 397-402 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). J Am Vet Med Assoc 232(8), 1186-1192 PubMed.
  • Louwerens M, London C A, Pedersen N C, Lyons L A (2005) Feline Lymphoma in the Post–Feline Leukemia Virus Era. J Vet Intern Med 19, 329-335 PubMed.
  • Kaser-Hotz B, Rohrer C R, Fidel J L et al (2001) Radiotherapy in three suspect cases of feline thymoma. J Am Anim Hosp Assoc 37 (5), 483-488 PubMed.
  • Smith A N, Wright J C, Brawner W R Jr. et al (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.
  • Reichle J K, Wisner E R (2000) Non-cardiac thoracic ultrasound in 75 feline and canine patients. Vet Radiol 41 (2), 154-162 PubMed
  • Shelton G D, Ho M, Kass P H (2000) Risk factors for acquired myasthenia gravis in cats: 105 cases (1986-1998). J Am Vet Med Assoc 216 (1), 55-57 PubMed.
  • Swainson S W, Nelson O L, Niyo Y et al (2000) Radiographic diagnosis: mediastinal parathyroid cyst in a cat. Vet Radiol Ultrasound 41 (1), 41-43 PubMed.
  • Day M J (1997) Review of thymic pathology in 30 cats and 36 dogs. J Sm Anim Pract 38 (9), 393-403 PubMed.
  • Forster-van-Hijfte M A, Curtis C F & White R N (1997) Resolution of exfoliative dermatitis and Malassezia pachydermatis overgrowth in a cat after thymoma resection. JSAP 38 (10),  451-454 PubMed.
  • Galloway P E, Barr F J, Holt P E et al (1997) Cystic thymoma in a cat with cholesterol-rich fluid and an unusual ultrasonographic appearance. JSAP 38 (5), 220-224 PubMed.
  • Malik R, Gabor L, Hunt G B et al (1997) Benign cranial mediastinal lesions in three cats. Aust Vet J 75 (3), 183-187 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.
  • Anilkumar T V, Voigt R P, Quigley P J et al (1994) Squamous cell carcinoma of the feline thymus with widespread apoptosis. Res Vet Sci 56 (2), 208-215 PubMed.
  • Ellison G W, Garner M M, Ackerman N (1994) Idiopathic mediastinal cyst in a cat. Vet Radiol 35 (5), 347-349 VetMedResource.
  • Gores B R, Berg J, Carpenter J L et al (1994) Surgical treatment of thymoma in cats: 12 cases (1987-1992). J Am Vet Assoc 204 (11), 1782-1785 PubMed.
  • Scott-Moncrieff J C, Cook J R Jr., Lantz G C (1990) Acquired myasthenia gravis in a cat with thymoma. J Am Vet Med Assoc 196 (8), 1291-1293 PubMed.

Other sources of information

  • Withrow & MacEwen’s (2020) Small Animal Clinical Oncology. 6th Edition. Saunders.
  • Ogilvie G K and Moore A S (1995) Thymoma in cats. In: Managing the veterinary cancer patient: a practice manual. Veterinary Learning Systems, Trenton N J,  pp 448-450.