Squamous Cell Carcinoma in the Cat

Superficial Facial Squamous Cell Carcinoma

Introduction

Squamous cell carcinoma (SCC) is a relative common tumor of the skin and mucocutaneous junctions in the cat. In the skin, it has been associated with ultraviolet light exposure of unpigmented skin. It is a tumor that affects the older cat and can have a protracted history.

Diagnosis

Diagnosis is obtained using the regular methods such as FNAB or pressure smears. If necessary, a wedge biopsy can be performed to obtain the final diagnosis. Adjunctive diagnostic imaging are useful with large nasal lesions or lesions in the medial canthus of the eye. Squamous cell carcinoma of the oral cavity needs to be worked up carefully, including FNAB of the local lymph nodes.

Therapy

Surgery is the main stay of therapy, although many other techniques have been described for local superficial lesions. Wide excision of the local tumour can be performed by several surgical techniques depending on the location of the tumour. Surgery in combination with radiotherapy or immunotherapy is worth further research in cases with extensive disease.

Full excision of the tumour is the method of choice to remove SCC. It is important to take sufficient margins around the tumour. This means that a pinna amputation or an amputation of the nasal planum is most commonly indicated. After resection a simple purse string suture will appose the cut edge around the open nasal cavity. The subcutaneous tissue is closed using a couple of interrupted sutures of with 4-0 Monocryl. The skin is closed with a continuous suture pattern of 4-0/5-0 nylon. Alternatives are cryosurgery, local irradiation and chemoablation.

Prognosis

The prognosis for SCC is good for superficial lesions, but one should be attentive for new lesions that may appear at predisposed spots. Aggressive surgical techniques for invasive disease may be curative or should be combined with adjunctive radiation or chemotherapy. Adjunctive therapy protocols have not been overly successful in invasive disease so far.

Oral Squamous Cell Carcinoma

Because of their relatively small body size and commonly late diagnosis of oral SCC, surgical treatment is considered impossible or unethical in most cats and is only performed in a very select group of smaller localized tumors. Palliative radiation protocols (consisting of 3–6 sessions of 6–10 Gy) and stereotactic radiation are not very effective with response rates of 39% or less and overall median survival times of 60 to 106 days. More recently, several case series of accelerated hypo-fractionated radiation therapy protocols with or without chemotherapy and/or surgery suggest improved outcomes. These protocols are labor intensive and require multiple anesthetic interventions. Chemo and immunotherapy have not been successful.

A ‘micro brachytherapy’ was developed in Utrecht as treatment option for inoperable tumors by direct intra tumoral injection of a suspension of radioactive ¹⁶⁶Ho­microspheres (Ø 10–30 µm). Local response rate was 55%, including complete response or partial response (downstaging) enabling subsequent marginal resection. Median survival time was 113 days overall and 296 days for patients with local response. Side effects were minimal. Tumour volume was a significant predictor of response.

References

1.  Withrow SJ. Cancer of the nasal planum. In: Withrow SJ, Vail OM, eds. Small Animal Clinical Oncology. St Louis, MO: Saunders; 2007:511–515.

2.  van Nimwegen SA, Bakker RC, Kirpensteijn J, van Es RJJ, Koole R, Lam MGEH, Hesselink JW, Nijsen JFW. Intratumoral injection of radioactive holmium (¹⁶⁶Ho) microspheres for treatment of oral squamous cell carcinoma in cats. Vet Comp Oncol. 2017; May 8. [Epub ahead of print]