Contributors: Laura Garrett, Rosanna Marsella, David Scarff

 Species: Canine   |   Classification: Diseases

Introduction Pathogenesis Diagnosis Treatment Outcomes Further Reading

Introduction

  • Skin mass of variable appearance depending on site and type.
  • Solitary or multiple.
  • Malignant are typically characterized by sudden onset of rapidly growing mass. Ulceration can be frequently seen in malignant tumors.

Incidence

  • Approximately 30% of total canine tumors.
  • Incidence of various types of tumors is somewhat affected by geographical location for tumors that are linked to UV exposure.
  • On average:
    • 55% are mesenchymal.
    • 40% are epithelial.
    • 5% melanocytic..

Presenting Signs

Epithelial

  • Basal cell carcinoma: common.
  • Squamous cell carcinoma: common.
  • Papilloma: common.
  • Adnexal:
    • Modified apocrine/ceruminous.
    • Apocrine/sweat gland: rare.
    • Sebaceous: common.
    • Hair matrix/follicle: rare.
    • Perianal: common in unspayed females.

Mesenchymal

  • Fibrosarcoma: common.
  • Fibroma: rare.
  • Lipoma: the most common tumor in dogs.
  • Hemangioma/hemgiosarcoma: uncommon.
  • Malignant fibrous histiocytoma: rare, except for vaccine-associated.

Canine round cell tumors

  • Melanocytic tumor: uncommon.
  • Mast cell tumor: common, reported to account for approximately 21% of all canine skin tumors.
  • Histiocytomas: common skin tumors of dogs:
    • One retrospective study over a 9-year period (1980-1989) showed that 5.5% of all cutaneous neoplasms were histiocytomas.
  • Plasmacytomas: rare.
  • Transmissible venereal tumors:
    • It is enzootic in many areas of the world including the southern United States.
  • Cutaneous lymphoma: while lymphoma is a common cancer in dogs, the cutaneous form is very rare and accounts for only 3-8% of all canine lymphomas.

Other tumors

Age Predisposition

  • In general, skin tumors are seen in older dogs (9-10 years).
  • Histiocytomas are most scommon in young dogs. Mean age of incidence being <3 years.
  • Transmissable venereal tumors are usually seen in young, sexually active dogs from an environment with a high concentration of free roaming dogs with poor control of reproduction.

Breed Predisposition

Pathogenesis

Etiology

  • Squamous cell carcinoma: exposure to sunlight and papilloma viruses. Development of squamous cell carcinoma is typically preceded by actinic keratosis.
  • Papilloma: papilloma viruses Papillomavirus that are transmitted by contact. Infection typically occurs when skin is damaged. Young or immunosuppressed dogs appear to be at increased risk.
  • Transmissible venereal tumors (TVT) are contagious, sexually transmitted tumors of dogs. Transmitted by direct contact wherein viable tumor cells are seeded onto mucous membranes.
  • Hemangiosarcoma and melanomas are also thought to be linked to UV exposure.
  • Others: unknown.

Pathophysiology

  • Primary mass may cause problems if very large or becomes ulcerated, secondarily infected or is at an irritaing site, eg eyelid Eyelid: neoplasia.
  • May be erosive or disfiguring. If malignant, may spread to local lymph nodes and/or distant sites.

Diagnosis

Presenting Problems

  • Solitary or multiple skin masses.
  • Secondary infection of ulcerated masses can be seen.

Client History

  • New mass or masses noticed in skin.
  • Slow or rapid growth reported may have had previous mass at same site - recurrence.

Clinical Signs

  • Solitary or multiple skin masses.
  • Well circumscribed, mobile, slow growing - suggests benign.
  • Poorly defined, adherent, rapid growth - suggests malignant.
  • May be ulcerated, erosive and secondarily infected lymph node enlargement possible.

Diagnostic Investigation

Cytopathology

  • Fine needle aspirate Fine-needle aspirate of primary mass for cytology (and lymph nodes if enlarged).
  • If mast cell tumor suspected, pre-medication with antihistamines is recommended.

Histopathology

  • Incisional, core or punch biopsy Biopsy: skin of primary mass for histopathology.
  • Exisional biopsy of a representative lesion if multiple skin masses.

Radiography

  • Three-view chest and abdominal radiographs or ultrasound to look for metastases. If nodules are identified in spleen and liver, it may be useful to aspirate them.

Gross Autopsy Findings

  • Solitary: abscess.
  • Inflammatory reaction.
  • Multiple: drug reaction.
  • Other skin disease.
  • Local/drainage lymph node enlargement if malignant.
  • Secondary mass/masses in other organs if malignant.

Histopathology Findings

  • Variable according to tumor type.
  • Will show degree of invasion, cell differentiation, etc and distinguish benign/malignant.

Treatment

Standard Treatment

Solitary mass

  • Wide surgical excision - if possible try to make diagnosis before surgery.
  • Radiotherapy Radiotherapy for some tumors (mast cell tumors/carcinomas/sarcomas) depending on site and ability to excize.

Multiple masses

  • Chemotherapy Chemotherapy: general principles for lymphoma Skin: epitheliotropic lymphoma (mycosis fungoides) and possibly mast cell tumors.
  • Mycosis fungiodes rarely responsive to treatment.
  • Combined surgery and radiotherapy for some solitary tumors depending on site, eg sarcoma.
  • Combined surgery and chemotherapy for some malignant tumors.

Subsequent Management

Treatment

  • Regular clinical examination to check for local recurrence and lymph node metastasis +/- radiography to check for distant metastasis.

Outcomes

Prognosis

  • Variable according to tumor type.
  • Grave for metastatic disease.

Expected Response to Treatment

Reasons for Treatment Failure

  • Not possible to treat because too extensive, or no effective therapy available, eg mycosis fungiodes.
  • Local recurrence due to inadequate excision.
  • Distant metastasis.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Stanclift R M & Gilson S D (2008) Evaluation of neoadjuvant prednisone administration and surgical excision in treatment of cutaneous mast cell tumors in dogs. JAVMA 232 (1), 53-62 PubMed.
  • Pakhrin B, Kang M S, Bae I H, Park M S, Jee H, You M H, Yoon B I, Choi Y K & Kim D Y (2007) Retrospective study of canine cutaneous tumors in Korea. J Vet Sci (3), 229-236 PubMed.
  • Mukaratirwa S, Chipunza J, Chitanaga S, Chimonyo M, Bhebhe E (2005) Canine cutaneous neoplasm: prevalence and influence of age, sex and site on the presence and potential malignancy of cutaneous neoplasms in dogs from Zimbabwe. J S Afr Vet Assoc 76 (2), 59-62 PubMed.
  • Kaldrymidou H, Leontides L, Koutinas S F, Saridomichelakis M N & Karayannopoulou M (2002) Prevalence, distribution and factors associated with the presence and the potential for malignancy of cutaneous neoplasms in 174 dogs admitted to a clinic in northern Greece. J Vet Med A Physiol Pathol Clin Med 49 (2), 87-91 PubMed.
  • Morris J S, Bostock D E, McInnes E F, Hoather T M, Dobson J M (2000) Histopathological survery of neoplasms in flat-coated retrievers, 1990 to 1998. Vet Rec 147 (11), 291-295 PubMed.

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