Squamous cell carcinoma

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Truncal carcinoma in the unpigmented skin of a dog[1]
Oral maxillary squamous cell carcinoma of a German Shepherd[2]
Pulmonary squamous cell carcinoma in a dog with secondary inspissated pus[3]

Squamous cell carcinoma (SCC) are one of the most common neoplasms of the dog.

These tumors originate in squamous epithelial cells located in the skin, kidneys and reproductive tact, intestines (oral to rectal) and mucosal surfaces of most organs, although the skin, oral cavity and digits are the most common sites in dogs.

Common locations of cutaneous squamous cell carcinomas include the legs, scrotum, perineum, inguinal region (truncal solar dermatitis), nasal planum, and various lightly pigmented areas.

Cutaneous squamous cell carcinomas are loosely categorized as follows:

  • Cutaneous squamous cell carcinoma (actinic/solar keratosis)
  • Subungual Squamous Cell Carcinoma
  • Oral squamous cell carcinoma
  • Multicentric SCC (Bowen's disease) - very rare in dogs[4]

These tumors generally grow slowly, but are locally invasive, commonly found in older dogs.

Although chronic inflammation plays an important role in the pathogenesis of squamous cell carcinoma[5][6][7], other factors are often involved. Ocular squamous cell carcinomas have been associated with canine papillomavirus[8], and cutaneous SCCs are commonly observed in the inguinal region of dogs due to UV exposure[9]. Urban pollutants may also increase the risk for tonsillar SCCs[10].

Epidemiological surveys show that oral SCCs are more prevalent in neutered female dogs, dogs aged 10 to <15 years, English Springer Spaniels and Shetland Sheepdogs[11].

Clinical signs depend on the organ involved, but localized ulceration, proliferative, raised cauliflower-shaped red plaques are a common finding. Digital SCCs commonly result in variable lameness and digital ulceration. Nasal tumors can cause nasal discharge and sneezing and oral SCCs usually present as ptyalism, gingival bleeding, anorexia, dysphagia and halitosis. Intestinal and rectal SCCs usual present with gastrointestinal signs; tenesmus, rectal bleeding and weight loss.

Regional lymphadenopathy is common as is secondary bacterial infections and pyoderma in cutaneous lesions. Metastases to bone are common and secondary osteomyelitis in such cases also occurs in some cases.

Diagnosis is usually confirmatory on visual inspection (via laparotomy with visceral tumors) and histopathological analysis of biopsied material. These tumors have a characteristic appearance under light microscopy, with islands, cords and trabeculae of invasive epithelial cells associated intimately with the overlying epidermis and breaching of the basal lamina zone. Keratin pearls (lamellae of keratin within the tumor) are commonly observed, formed by the invasive cells.

Immunohistochemistry usually shows binding to calretinin and cytokeratins[12].

Histological classifications include:

  • papillary squamous cell carcinoma
  • basaloid squamous cell carcinoma
  • adenosquamous carcinoma
  • spindle cell carcinoma

A differential diagnosis would include mast cell tumor, fibrosarcoma, melanoma and in visceral organs, lymphoma.

Treatment in localized skin lesions is usually curative but recurrence in adjacent areas is not uncommon.

Adjunct therapy such as cryotherapy, radiation therapy, photodynamic therapy and intratumoral chemotherapy may assist recovery and recurrence.

Intratumoral 5-fluorouracil, cisplatin[13], docetaxel and cyclosporine have been used in the past with some success[14].

With oral maxillary squamous cell carcinoma, curative responses are uncommon, but palliative treatment may be obtained with radiation therapy combined with carboplatin and doxorubicin[15].

Because of the role of inflammation in the pathogenesis and propagation of these tumors, the judicious use of NSAIDs is recommended, such as carprofen or meloxicam long-term.

References

  1. Your own vet
  2. Vetlearn
  3. Uni of Pennsylvania
  4. Baer KE & Helton K (1993) Multicentric squamous cell carcinoma in situ resembling Bowen’s disease in cats. Vet Pathol 30(6):535-543
  5. Hargis AM et al (1977) Chronic dermatosis and cutaneous squamous cell carcinoma in the beagle dog. Vet Pathol 14:218-228
  6. Zur G (2005) Bilateral ear canal neoplasia in three dogs. Vet Dermatol 16(4):276-280
  7. Ward DA et al (1987) Squamous cell carcinoma of the corneoscleral limbus in a dog. JAVMA 190(11):1430-1432
  8. Tomo Wiggans K et al (2012) Malignant transformation of a putative eyelid papilloma to squamous cell carcinoma in a dog. Vet Ophthalmol Aug 9
  9. Waropastrakul S et al (2012) Infrequent detection of papillomaviral DNA within canine cutaneous squamous cell carcinomas, haemangiosarcomas and healthy skin on the ventrum of dogs. Vet Dermatol 23(3):197-241
  10. Withrow SJ & Vail DM (2006) Withrow and MacEwen’s Small Animal Clinical Oncology. 4th ed. Philadelphia: WB Saunders
  11. Nemec A et al (2012) Histological subtypes of oral non-tonsillar squamous cell carcinoma in dogs. J Comp Pathol 147(2-3):111-120
  12. Fulton A et al (2012) The expression of calretinin and cytokeratins in canine acanthomatous ameloblastoma and oral squamous cell carcinoma. Vet Comp Oncol Sep 18
  13. Kitchell BK et al (1995) Intralesional sustained-release chemotherapy with therapeutic implants for treatment of canine sun-induced squamous cell carcinoma. Eur J Cancer 31A(12):2093-2098
  14. Waite A et al (2012) Phase II study of oral docetaxel and cyclosporine in canine epithelial cancer. Vet Comp Oncol Aug 21
  15. Mestrinho LA et al (2012) Neoadjuvant chemoradiotherapy and surgery as treatment for oral maxillary squamous cell carcinoma in a dog. Aust Vet J 90(7):264-268
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