+ Biologic Behavior

  • Nasal planum SCC is common in cats and rare in dogs
  • Tumors: LSA, FSA, hemangioma, melanoma, MCT, and fibroma
  • Non-neoplastic conditions of the nasal planum include eosinophilic granuloma and immune-mediated disease
  • SCC associated with ultraviolet irradiation (UVA and UVB) from sunlight
  • Damaging photochemical effects of sunlight are related to hair density, wave length, and intensity of radiation
  • Genetic inheritance is related to distribution of keratin and melanin and quantity of Langerhans cells
  • White-haired cats have 13.4-times greater risk of developing SCC than cats of other coat colours
  • Non-white-haired cats develop SCC in areas of poor pigmentation and poorly haired areas
  • Melanin protects skin against solar energy
  • Role of FeLV and FIV is unknown, but 24% (7/29) cats with FIV have concurrent SCC
  • Tumor-suppressor gene p53 mutations found in 82% (9/11) cats with pinna SCC and 50% (7/14) with other SCC
  • Histologic type depends on the timing of biopsy: carcinoma in situ, superficial SCC, and deeply infiltrative SCC
  • Locally invasive tumor but rarely metastasize

+ Clinical Signs

  • Progression of clinical signs:
  • Crusty and erythematous lesion
  • Superficial erosion and ulceration (i.e., carcinoma in situ or early SCC)
  • Deeply invasive and erosive lesion
  • SCC originates from cornified external surface of nasal planum in cats and mucous membrane of nostril or nasal planum in dogs
  • other sites in cats include head and neck (especially pinna and eyelids) (>80%) with multiple lesions in 30%

+ Diagnosis

  • Wedge or incisional biopsy of erosive or proliferative lesions to determine histology and depth of invasion
  • General anesthetic usually required due to sensitivity of nasal planum
  • Impression smears or superficial biopsies are rarely useful due to superficial inflammation which frequently accompanies both SCC and non-neoplastic lesions
  • Regional and thoracic radiographs are rarely indicated
  • CT or MRI of the nose is important to determine caudal extent of tumor and planned resection in dogs

+ Palliative Management

  • Progression of preneoplastic lesions may be minimized or prevented by limiting exposure to ultraviolet light
  • Tattoo and sunscreen are rarely helpful in preventing SCC

+ Surgery

  • Nasal planum resection is the most effective treatment for invasive SCC (i.e., T3 and T4) of the nasal planum
  • Closure: skin-to-mucosal apposition or purse-string suture
  • Inappetence for up to 3 days postoperatively but enteral feeding is rarely required
  • Scab forms over surgery site but healing usually complete by 4 weeks
  • Nasal planum resection is associated with acceptable cosmetic results and good functional results:
  • Median DFI 594 days for nasal planum lesions alone and 426 days when concurrent with pinna SCC
  • Local tumor recurrence 57% (4/7) cats with incomplete excision and 33% (1/3) cats with complete excision, with 12-month DFI > 80%
  • MST 673 days for nasal planum lesions alone and 530 days when concurrent with pinna SCC
  • Complication: nasal stenosis (treatment options include wide skin excision and resection of rostral nasal septum, laser ablation, rubber stents, or permanent placement of stainless steel intraluminal expansile stents)
  • Combined resection of premaxilla-maxilla and nasal planum

+ Radiation Therapy

  • Radiation can be delivered either as local or external beam therapy
  • Local radiation therapy with strontium-90 is indicated for cats with superficial SCC as strontium does not penetrate > 2 mm, with 1-year DFI 89%, 3-year DFI 82%, and median DFI 34 months
  • External beam radiation therapy can be used for superficial and deep lesions
  • Median DFI 361 days to 16.5 months
  • 1-year DFI 60%-64% and 5-year DFI 10%
  • MST 383-946 days with proton beam irradiation
  • T is and T 1 SCC have significantly better tumor control with 56% 5-year DFI

+ Cryosurgery

  • Cryosurgery is indicated for cats with superficial, small and non-invasive SCC
  • Disadvantage: margins are difficult to determine
  • Cryosurgery response is site dependent with 100% eyelid and pinna lesions resolving after 1 treatment, but 19% of nasal planum SCC failing to respond after 2-3 treatments
  • Median DFI 254 days
  • Local tumor recurrence rate 17%-73% (8/11) with 1-year DFI 84% and 3-year DFI 81%
  • MST 682 days

+ Photodynamic Therapy

  • Photodynamic therapy is indicated for superficial tumors (< 3-4 mm deep) due to limited penetration of wavelength of light used to activate photosensitizer
  • Disadvantage: margins are difficult to determine
  • Photodynamic therapy involves administration of photosensitizer that is preferentially retained by tumor tissue and results in formation of oxygen free radicals when irradiated with light of wavelength absorbed by photosensitizer
  • 77%-85% response rate with DFI 3-18 months for responders
  • Response rate is better for:
  • Superficial lesions with 75%-100% CR for Tis and T1 lesions but < 30% for higher grade lesions
  • Small lesions (< 5.0 cm)
  • Topical 5-aminolevulinic acid cream and subsequent exposure to red light of wavelength 635 nm has been used in 13 cats with cutaneous SCC with an 85% CR after 1 treatment but 64% local tumor recurrence rate after a median 21 weeks
  • Complications include no exposure to sunlight for minimum 2 weeks and facial edema, erythema, and necrosis which can be slow to resolve over 3-6 weeks

+ Intralesional Chemotherapy

  • Cytotoxic agents have been combined with substances such as sesame oil, bovine collagen, and epinephrine to prevent or minimize systemic absorption and increase local concentration of chemotherapy
  • Cytotoxic agents that have been investigated include carboplatin, cisplatin, and fluorouracil
  • 73.3%-83.0% overall response rate with 64.0%-73.3% CR and 19.0% PR
  • No evidence of systemic toxicity

+ Systemic Chemotherapy

  • Carboplatin: 210-240 mg/m 2 IV q 3-4 weeks
  • Doxorubicin (20-30 mg/m 2 IV q 3 weeks) and bleomycin (10 IU/m 2 IM or IV for 4 days then once weekly) has resulted in sustained remission in 25% (1/4) cats with metastatic SCC

+ Immunotherapy

  • Retinoids, or synthetic derivatives of vitamin A, increase epithelial differentiation
  • Retinoids may reverse or limit preneoplastic lesions but are rarely effective against advanced lesions
  • Carotenoid therapy (i.e., β-carotene and canthaxanthin) improves solar dermatitis in 75% (9/12) cats
  • Isotretinoin (13-cis-retinoic acid) or etretinate are not effective for cats with SCC with only 1 (6.7%) of 15 precancerous or SCC lesions responding to therapy
  • Recombinant feline IFN has marked antitumor affect against SCC in vitro