Page 1418 - Clinical Small Animal Internal Medicine

1356 Section 11 Oncologic Disease

Ear canal tumors often require advanced imaging with incompletely resected tumors of the ear canal,
VetBooks.ir studies to determine operability and extent of surgery regardless of histologic type of tumor.
Topical 5% fluorouracil cream may be applied to super­
necessary, or to plan for radiotherapy adjunctively
or as primary treatment of nonresectable, invasive
common practice in human dermatologic oncology. This
lesions. ficial squamous or basal cell lesions in dogs, as is the
agent is applied topically twice daily by gloved finger or
cotton swab applicator for 3–6 weeks. Significant local
Therapy irritation and inflammation are seen as part of the thera­
peutic response. Dogs should be prevented access to the
Most skin tumors are best addressed by local surgical treated site, as licking the topical cream can be harmful
excision. Benign lesions of the skin can be excised with to oral mucosa and may be toxic systemically. Critically,
modest margins to affect a cure in most cases. Surgical fluorouracil should never be applied to cats, as even
excision allows for accurate diagnosis, histologic grad­ topical application can result in lethal neurotoxicity in
ing, and surgical margin assessment, which can guide this species.
further adjunctive therapy if necessary. However, surgery Topical immunotherapy for superficial squamous
can be disfiguring, particularly when the lesion arises on cell carcinomas may be attempted. Imiquimod 5% cream
the head and face. Squamous cell carcinoma of the ear is a nonspecific active immunotherapeutic agent that
tips can be managed by pinna amputation in cats. Nasal induces a strong macrophagic response when topically
planum resection can also be curative in cats, although applied. This immunostimulant causes inflamed, crusted
surgery of SCC of the nasal planum in dogs is often and scabbed lesions to arise in the treated area, which is
unsuccessful in controlling local disease. Surgery is the basis of the therapeutic effect. Imiquimod is applied
always the best primary modality for treatment of topically to superficial lesions once daily, or in sensitive
any cancer, but owners may balk at the degree of disfig­ cases three times weekly, for 3–6 weeks.
urement the dog or cat experiences with nasal planum Intralesional therapy with chemotherapy in sesame oil
resection. or purified bovine collagen matrix for depot delivery has
Serial resection of squamous cell carcinoma or also been described in the literature. Agents such as
hemangiosarcoma, while still small, dermal and arising carboplatin, cisplatin, bleomycin, and fluorouracil have
on glabrous skin, is recommended for dogs with field all been introduced intratumorally with sometimes
carcinogenesis from sunlight exposure. Highly invasive striking results.
or large field lesions of the ventral abdomen, prepuce, Systemic therapy with retinoic acid derivatives such as
and medial thighs of such dogs may be less amenable to 13‐cis‐retinoic acid or isotretinoin has been attempted
surgical excision. In these cases, radiation therapy deliv­ as a cellular differentiation or cytotoxic strategy in
ered to the local tumor site, or tumor site plus regional canine and feline skin tumors, particularly squamous
nodes, may be curative. Radiation therapy for skin cell and infundibular keratinizing acanthoma (keratoa­
tumors may involve traditional fractionated megavolt­ canthoma). Retinoid therapy has been reported in the
age irradiation with curative intent, or may be delivered literature to have mixed success.
as palliative fractionated therapy. Superficial radiation, The use of COX‐2 inhibitors has shown modest effi­
such as delivered through topical plesiotherapy using a cacy in treatment of squamous cell carcinomas of the
strontium‐90 probe, is highly effective for small, nonin­ oral cavity, and thus may be helpful in cutaneous SCC
vasive lesions. Photodynamic therapy utilizing laser treatment as well. The COX‐2 inhibitor nonsteroidal
light to activate photosensitizing agents is a common antiinflammatory drugs (NSAIDs) have both antiangio­
treatment for human skin cancer patients, although genic and immunomodulatory effects, and are generally
the technology is less readily available to veterinary helpful in pain control for veterinary patients. Similarly,
medicine. the newer class of agents called receptor tyrosine kinase
Ear canal tumors generally require surgical excision, inhibitors (toceranib, masitinib, imatinib) are inhibitors
which may entail vertical canal ablation in the case of of cell signaling. These agents are promiscuous receptor
superficial benign tumors, but more likely requires a signaling blockers and may modulate tumor regression
more aggressive surgical approach with total ear canal through inhibition of vascular endothelial growth factor
ablation and lateral bulla osteotomy. Extensive surgery (VEGF) and platelet‐derived growth factor (PDGF)
was associated with long median survivals in both dogs receptors, thus acting as antiangiogenic agents. The
and cats (>36 months and 50.3 months, respectively). therapeutic concept referred to as metronomic chemo­
Mitotic rate was prognostic for a series of ear canal therapy employs smaller daily or alternate‐day dosing of
tumors, with a mitotic index of 2 or less being more NSAIDs, low‐dose cytotoxic agents such as cyclophos­
favorable. Radiation therapy may be required for patients phamide, chlorambucil, or lomustine, often combined