Page 379 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 19 Tumors of the Skin and Subcutaneous Tissues 357

Squamous Cell Carcinoma in Situ

VetBooks.ir SCC in situ is defined as a carcinoma that has not penetrated
the basement membrane of the epithelium. In some cases it is
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thought to be caused by Felis catus papillomavirus infection.
When it appears in multiple sites, it is also known as Bowen’s
carcinoma, BISC, or multicentric PPV–induced SCC. This
disease is seen primarily in cats, with only a few reports in
dogs. 6,51,96–98 Actinic keratosis is the name typically used for
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SCC in situ that arises as a consequence of UV exposure. Dif-
ferentiation of actinic keratosis from BISC is based on location
and histopathologic appearance.
Clinically SCC in situ can present as erosions of the epider-
mis, proliferations, or crusted plaques. They may be painful
on palpation. BISC lesions can occur anywhere on the body,
on both haired and unhaired skin, and in areas with and with-
out sun exposure (Fig. 19.2). Solitary lesions are unusual. 6,97
Actinic keratosis, on the other hand, occurs in lightly haired
skin with UV exposure, and these lesions are often solitary.
Actinic keratosis typically is accompanied by solar elastosis and
fibrosis of the skin, consistent with the effects of chronic UV • Fig. 19.2 Plaquelike lesion of Bowen’s in situ carcinoma on the head of
exposure. By definition, carcinoma in situ is not yet invasive a cat. Multiple such lesions may be present on the patient. (Courtesy Dr.
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and so metastasis has not occurred. However, left untreated, Rodney Rosychuk.)
carcinoma in situ can progress to invasive carcinoma and put
the patient at risk for metastasis. Patients with BISC typically
continue to develop new lesions over time, but metastasis is These tumors typically occur in cats older than 10 years of age
uncommon. 6,51,96–98 and at a median age of 10 to 11 years in dogs. 6,38,105 Cats have a
Many treatment approaches are effective for solitary SCC predilection for developing these tumors on their heads, particu-
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in situ. Surgical excision is the treatment of choice for most larly in lightly haired areas of white cats. This predilection reflects
lesions. The median disease-free interval (DFI) and survival the role of UV light in the induction of many of these tumors.
time (MST) in 39 cats treated with surgical excision for single A decreased risk has been reported in Siamese, Himalayan, and
nasal and pinna lesions were 594 days and 675 days, respec- Persian breeds. 6,92 Labrador and golden retrievers may have a pre-
tively. Strontium-90 plesiotherapy in 14 cats with SCC in disposition for the development of nasal planum SCC. 106 Blood-
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situ of the nasal planum resulted in 14 complete responses hounds, basset hounds, and standard poodles may be predisposed
(CRs) with no recurrences and an overall survival time of to develop cutaneous SCC. 105
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>3000 days. As expected, metastasis appears rare in cats with The clinical presentation of cutaneous SCC can be highly vari-
SCC in situ/actinic keratosis; in 61 cats with SCC of the nasal able. Cutaneous SCC can appear plaquelike to papillary and from
planum and pinnae, only one cat eventually developed metas- crateriform to fungiform. These lesions may be erythemic, ulcer-
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tasis to the regional LN. 23 ated, or crusted. Paraneoplastic hypercalcemia has been reported
BISC lesions are often multifocal. As a result, marginal in three cats with cutaneous SCC, two with ear canal tumors, and
surgical resection is primarily indicated to improve comfort one with multiple cutaneous tumors. 107,108 Metastasis at the time
and local control when other therapies are no longer effective. of death was present in 6 of 15 cats with invasive SCC of the nasal
Imiquimod cream (5%) has been reported to be effective in planum, with the most common metastatic sites being regional
treating BISC in 12 cats, with five cats having at least one LNs and the lungs. 109 Metastasis in dogs with cutaneous SCC
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lesion undergo a complete response (CR). Most cats were appears rare, with only four dogs described in the literature. 35,110
treated with daily application, although some were treated Four of 17 dogs with SCC of the nasal planum had regional
three times per week. One study on the use of 13-cis-retinoic metastasis to the mandibular LNs. 106 Metastasis to distant sites
acid for SCC in situ did not demonstrate clinical efficacy in was not reported.
cats with BISCs or SCCs. 100 Etretinate showed some prom- Treatment for cutaneous SCC is primarily surgical when
ise for the treatment of SCC in situ and for invasive SCC, feasible. Wide surgical excision results in long-term control in
but this drug is no longer available. 101 Photodynamic therapy both dogs and cats. In a series of 61 cats treated with surgery,
(PDT) is also effective in the treatment of BISC in people and RT, and cryosurgery, surgery resulted in the longest median
cats, with reported response rates up to 100%. 102–104 With DFI at 594 days, although many of these cats may not have had
PDT, the clinical stage of the tumor was prognostic for sur- invasive disease. Complete surgical excision of nasal planum
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vival. One author (MH) has treated a cat with BISC with pal- SCC in dogs resulted in long-term control in four of six dogs;
liative RT, and partial response/ stable disease was achieved two dogs with incomplete excision developed local recurrence
for 8 months. (see Chapter 24, Section A, for further discussion of nasal pla-
num tumors). 111
Squamous Cell Carcinoma Little data is available on the use of chemotherapy to treat
cutaneous SCC in dogs and cats. Carboplatin compounded
SCC is a malignant tumor of the epidermis in which the cells with sterile sesame oil injected into nasal planum SCCs in
demonstrate differentiation to squamous cells (keratinocytes). 105 cats resulted in a CR rate of 73% and a 55% progression-free