+ 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



T0 No evidence of neoplasia
Tis Carcinoma in situ - Primary Tumor
T1 Tumor less than 2 cm in diameter, superficial, and exophytic
T2 Tumor 2-5 cm in diameter or with minimal invasion irrespective of size
T3 Tumor > 5 cm in diameter or with invasion of subcutis irrespective of size
T4 Tumor invades other structures such as fascia, muscle, bone, or cartilage
M0 No evidence of metastasis
M1 Evidence of distant metastasis with site specified - Metastasis
N0 No evidence of regional lymph node involvement
N1 Movable ipsilateral lymph node with (a) no tumor and (b) tumor - Node
N2 Movable contralateral lymph node with (a) no tumor and (b) tumor
N3 Fixed regional lymph node