Skin: neoplasia

• Second most common site for feline tumors.
• Skin tumors in cats make up 20-30% of all tumors.
• Less common than in dogs.
• Fewer different types occur but higher percentage is malignant. Malignant skin tumors in cats are reported to be three times more common than benign tumors.
• Relative frequency of various skin tumors has been reported to be changing with fibrosarcoma becoming more common than epithelial skin tumors.

• Skin mass of variable appearance depending on site and type.
• Solitary or multiple.

Incidence

• Approximately 20-30% of all feline tumors.
• Main tumors are basal cell tumor, squamous cell carcinoma, fibrosarcoma and mast cell tumor.

Epithelial

• Basal cell carcinoma - common.
• Squamous cell carcinoma - common.
• Papilloma - rare.
• Adnexal.
  • Modified apocrine/ceruminous.
  • Apocrine/sweat gland - uncommon.
  • Sebaceous - rare.
  • Hair matrix/follicle - rare.
  • Perianal - rare.

Mesenchymal

• Fibrosarcoma - common.
• Fibroma - rare.
• Lipoma/liposarcoma - uncommon.
• Hemangioma/hemangiosarcoma - uncommon.
• Malignant fibrous histiocytoma - rare, except for vaccine-associated.

Mastocytoma

• Mast cell tumor - common.

Melanoma

• Melanocytic tumor - uncommon to rare.

Multiple masses

• Mast cell tumor - common.
• Cutaneous lymphoma -uncommon.
• Metastatic skin lesions - uncommon.
• Squamous cell carcinoma (solar) - common in certain areas (high altitude).
• Mycosis fungoides - rare.

• Older cats (9-10 years).

• No breed predilection overall (Siamese Siamese - less affected with squamous cell carcinoma and more affected with mast cell tumors).

• Squamous cell carcinoma - exposure to sunlight.
• Metastatic carcinoma:
  • Pancreatic Pancreas: disease - overview - rare.
  • Bronchogenic carcinoma Lung: pulmonary neoplasia - metastasize to digits (uncommon).
• Fibrosarcoma - vaccination has been considered as risk factor Feline injection-site associated sarcoma.
• Others - unknown.

Specific

• Squamous cell carcinoma - white hair on face, common sites pinna   , nasal planum   .
• Fibrosarcoma - commonly at injection sites.

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

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

• Solitary or multiple skin masses.
• If masses become ulcerated, they may develop infections.
• Solar squamous cell carcinoma can appear as scab   and develops to an erosive lesion   rather than a mass.

• New mass or masses noticed in skin.
• Slow or rapid growth reported may have had previous mass at same site - recurrence.
• Typically no pain is associated with it.
• Pruritus can be present with some tumors (eg mast cell tumors) or if infection develops.

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

Cytopathology

• Fine needle aspirate  Fine-needle aspirate of primary mass for cytology (and lymph nodes if enlarged).
• If mast cell tumor is suspected, premedication with antihistamines should be considered before fine needle aspirate.

Histopathology

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

Radiography

• Three-view chest Radiography: thorax and abdominal Radiography: abdomen radiographs or ultrasound to look for distant metastases.

• Solitary - abscess Abscess.
• Inflammatory reaction.
• Eosinophilic granuloma Eosinophilic granuloma complex.
• Multiple - drug reaction Drug eruption   .
• Other skin disease.
• Local/drainage lymph node enlargement if malignant.
• Secondary mass/masses in other organs if malignant.

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

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.
• Highly proliferative tumors (eg fibrosarcomas) should be followed by radiotherapy whenever possible. 

Multiple masses

• Chemotherapy Chemotherapy; general principles for lymphoma Lymphoma (mycosis fungoides) and possibly mast cell tumors Mastocytoma.
• Mycosis fungoides rarely responsive to treatment.

• Combined surgery and radiotherapy for some solitary tumors depending on site.
• Combined surgery and chemotherapy for some malignant tumors.
• Immunotherapy with cells (eg VERO cells) genetically modified to produce cytokines is a novel and prosing approach for highly malignant tumors.

Monitoring

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

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

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

Refereed papers

• Recent references from PubMed and VetMedResource.
• Miller M A, Nelson S L, Turk J R et al (1991) Cutaneous neoplasia in 340 cats. Vet Pathol 28 (5), 389-395 PubMed.
• Bostock D E (1986) Neoplasms of the skin and subcutaneous tissues in dogs and cats. Brit Vet J 142 (1), 1-19 PubMed.
• Susaneck S J (1983) Feline skin tumors. Compend Contin Educ 5 (4),  251-258 VetMedResource.
• Macy D W & Reynolds H A (1981) The incidence, characteristics and clinical management of skin tumors of cats. JAAHA 17 (6), 1026-1034 VetMedResource.
• Scott D W (1980) Feline Dermatology 1900-1978: a monograph. JAAHA 16 (3), 331-459 VetMedResource.

Other sources of information

• Guaguere E & Prelaud P (1999) A practical guide to feline dermatology.Merial.
• Carpenter J L, Andrews L K and Holzworth J (1987) Tumors and Tumor-like lesions. In: Diseases of the Cat. Medicine and Surgery. Ed J Holzworth. Philadelphia: W B Saunders Co. pp 406-596.
• Vail D M and Withrow S J (1996) Tumors of the skin and subcutaneous tissues. In: Small Animal Clinical Oncology. Eds S J Withrow and E G MacEwen. 2nd edition. Philadelphia: W B Saunders Co. pp 167-191.