+ Etiology

• SCC accounts for 5% of canine skin tumors and 15% of feline skin tumors
• Predisposition to unpigmented or lightly pigmented skin exposed to solar radiation
• Firm and nodular masses which may be either proliferative or erosive and extend deeply into the dermis
• 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
• Sites: head and neck (especially pinna, nasal planum, and eyelids) (>80%) with multiple lesions in 30%
• Siamese cats under-represented

+ Biologic Behavior

• Locally aggressive but metastasize late in the course of disease
• Metastasis in advanced and poorly differentiated SCC
• Paraneoplastic hypercalcemia has been reported in 2 cats

+ Histopathology

• Keratosis: small, reactive proliferation of keratinocytes which do not invade dermis
• Actinic keratosis: secondary to sun exposure, may invade underlying dermis, and considered preneoplastic
• Carcinoma in situ: non-invasive carcinoma confined to the epidermis
• SCC are usually well-differentiated, but poorly differentiated, acantholytic, and spindle-cell SCC have been reported

+ Surgery

• Surgery is the most effective treatment for invasive SCC (i.e., T3 and T4) of the pinna and nasal planum
• Surgical techniques: pinnectomy and nasal planum resection
• Pinnectomy is associated with acceptable cosmetic results
• Median DFI 19 months
• Local tumor recurrence in 100% (2/2) cats with incomplete excision and 23% (12/52) cats with complete excision
• 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

+ Cryosurgery

• 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

+ Laser Surgery

Laser surgery with Nd:YAG laser successful in 1 cat with no local tumor recurrence in 30 months

+ 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

+ 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

+ Non-Toxic Agents

• 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