Equine Skin Neoplasms

General considerations

The following is reported by Schaffer et al (2013)

  # %
Sarcoid 1,543 46
SCC 633 19
SCC in situ 28 1
Melanoma 344 10
Soft tissue sarcoma 238 7
Squamous papilloma 189 6
Benign soft tissue 114 3
Fibroma 80 2
Lipoma 21 1
Hemangioma 7 .2
Leiomyoma 3 0.1
Myxoma 3 0.1
Mast cell tumor 99 3
Lymphoma 57 2
Giant cell tumor 35 1
Hemangiosarcoma 20 1
Epithelial tumors 51 0.4
Basal cell tumor 39 1
Carcinoma 8 0.2
Apocrine tumor 4


Schaffer PA, Wobeser B, Martin LE, Dennis MM, Duncan CG. Cutaneous neoplastic lesions of equids in the central United States and Canada: 3,351 biopsy specimens from 3,272 equids (2000-2010). J Am Vet Med Assoc. 2013 Jan 1;242(1):99-104. doi: 10.2460/javma.242.1.99. PMID: 23234288.

Epithelial neoplasms

Mesechymal tumors

Equine Sarcoid

There are 6 different clinical presentations of sarcoid - they all look similar histologically

  1. occult
  2. verrucose
  3. nodular
  4. fibroblastic
  5. mixed
  6. malignant

Bovine papillomavirus-1 (Deltapapillomavirus) and sometimes BPV-2 are external factors in the development of sarcoid. Horses dont have the immunological ability to remove infection.

About half of the horses, especially those in contact with cattle, have BHV-1 DNA in normal skin.

The characteristic changes histologically are adn infiltrative stromal tumor with proliferation of fibroblastic cells in contact with an epidermis that has prominent rete ridges that insert into the fibroblastic cells.


Ogłuszka M, Starzyński RR, Pierzchała M, Otrocka-Domagała I, Raś A. Equine Sarcoids-Causes, Molecular Changes, and Clinicopathologic Features: A Review. Vet Pathol 2021; 58: 472-482.

Vascular tumors

The horse has a propensity to develop vascular tumors that are interesting excercises in characterisation. Vascular hamartoma, hemangioma and angiomatosis are all reported, and often the photomicrographs look similar. Wise et al (2021) published a detailed discussion of one such tumor in the horse.


Wise LC, Crosby DE, Walton AN, Neef A, Shearer PL, Woodward DJ, Hilbert BJ. A tumour of vascular origin in a horse. Equine Vet Educ 2021; 33: e353-e356.


Round cell tumors


Nerve sheath Tumors


Schöniger and Summers reported on 2 horses with nerve sheath tumors - neurofibroma. Their criteria were:

Subtypes are localized or plexiform (multinodular) then classic, collagenous, cellular and pigmented.
Neurofibromas have buckled or wavy nuclei – S100 cells are Schwann cells which are part of the tumour.
Are composed of Schwann cells, neurofibrocytes and perineural cells.
Subtypes are localized, plexiform or diffuse (infiltrative) then then classic, collagenous, cellular and pigmented.

Schöniger S; Summers BA(2009) Localized, Plexiform, Diffuse, and Other Variants of Neurofibroma in 12 Dogs, 2 Horses, and a Chicken. Vet Pathol 2009 46: 904-915.

Other neoplasms

Melanocytic tumors




Sullins KE. Melanocytic tumours in horses. Equ Vet Educ 2020; 12:624-630