Skin: fibroma / fibrosarcoma in Horses (Equis) | Vetlexicon
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Skin: fibroma / fibrosarcoma

ISSN 2398-2977

Contributor(s) :


  • Uncommon tumor of dermal or subcutaneous origin, however one of the most common neoplasms in the frog of the horse's foot.
  • 12.5% of fibrosarcomas were found in the skin in one report.
  • Cause: unknown.
  • Signs: nodules in dermis or subcutaneous tissue +/- ulceration.
  • Diagnosis: histopathology.
  • Treatment: surgical excision.
  • Prognosis: fibroma: good; fibrosarcoma: guarded.

Presenting signs

  • Solitary nodules.
  • Distribution: neck, flanks, legs.

Age predisposition

  • Fibrosarcomas may occur in horses of any age.


Predisposing factors


  • Fibrosarcoma has been reported to arise in burn wounds of a horse.


  • Unknown.
  • Fibroma considered a benign lesion.
  • Fibrosarcoma are locally invasive, metastasis in 25% of cases.


Presenting problems

  • Nodules.

Client history

  • Lump under skin on neck, flanks, legs.
  • Size unchanged since first noticed (fibroma) or gradually getting larger (fibrosarcoma).

Clinical signs

  • Solitary nodules.
  • Distribution: neck, flanks, legs.


  • Nodules in dermis or subcutaneous tissue.
  • Firm or soft.
  • Well-circumscribed.
  • Surface may be hyperkeratotic in the early stages.


  • Nodules in subcutaneous tissue.
  • Firm.
  • Poorly demarcated.
  • Infiltrate surrounding tissue.

Fibromas or fibrosarcomas

  • Ulceration of tumor surface Skin: neoplasia - fibrosarcoma.
  • Fleshy growths of frog.

Diagnostic investigation


Confirmation of diagnosis

Discriminatory diagnostic features

  • Clinical signs.

Definitive diagnostic features

  • Histopathology.

Differential diagnosis

  • Sarcoid Sarcoid.
  • Other cutaneous neoplasms.
  • Eosinophilic granuloma.
  • Exuberant granulation tissue.
  • Foreign body reaction.
  • Bites and stings Insect hypersensitivity.
  • Bacterial granuloma.
  • Actinomycotic mycetoma.
  • Dermatophytosis Dermatophytosis.
  • Eumycotic mycetoma.
  • Pheohyphomycosis.
  • Sporotrichosis.
  • Mast cell tumors Skin: neoplasia - mast cell tumor.
  • Dermoid cyst.
  • Tuberculosis.
  • Axillary nodular necrosis.
  • Calcinosis circumscripta.
  • Nodular panniculitis.


Initial symptomatic treatment

  • Total excision biopsy - therapy of choice.

Standard treatment

  • Surgical excision.

Lesions that are difficult to surgically resect





  • Good: low recurrence rate after surgical excision.


  • Guarded: recurrence or metastasis following surgical excision.

Expected response to treatment

  • Surgical excision: no recurrence.
  • Radiotherapy: regression.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Voute L C (2010) Fibro-osseous tumours in the horse: A reminder of the importance of a multidisciplinary approach to diagnosis. Equine Vet Educ 22 (1), 66 WileyOnline.
  • Pieber K, Kuebber-Heiss A, Kuebber P & Kofler J (2010) Fibro-osseous tumour of the fourth metacarpal bone in a horse: Clinical, radiographic and long-term post operative findings. Equine Vet Educ 22 (2), 62-65 VetMedResource.
  • Trostle S S et al (2005) Juvenile mandibular ossifying fibroma in a 12-week-old foal. Equine Vet Educ 17 (6), 284-286 VetMedResource.
  • Henson F M D & Dobson J M (2004) Use of radiation therapy in the treatment of equine neoplasia. Equine Vet Educ 16 (6), 315-318 VetMedResource.
  • Hikita M, Ishikawa Y, Shibahara T & Kadota K (2004) Mesenteric myofibroblastoma in a horse. Vet Rec 154 (25), 795-796 PubMed.
  • Roels S et al (1998) Successful treatment of an equine preputial fibrosarcoma using 5-fluorouracil/evaluation of the treatment using quantitative PCNA and Ki67 (MIB 1) immunostaining (Case report). Zentralbl Veterinarmed A 45 (10), 591-598 PubMed.
  • Schooley E K et al (1998) Musculoskeletal system neoplasia. Vet Clin North Am Equine Pract 14 (3), 535-542 (Review) PubMed.

Other sources of information

  • Knottenbelt D C, Patterson-Kane J C & Snalune K L (2015) Clinical Equine Oncology. Elsevier, UK.