Page 465 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 23 Cancer of the Gastrointestinal Tract 443

In one series of 39 dogs with oral SCC, the overall median PFS time 217 days after hemimandibulectomy, and 192 days when more
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was 36 months, with 1- and 3-year PFS rates of 72% and 55%, than 50% of the mandible was resected. Expansile, blastic, and
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respectively. Local tumor control was more successful with smaller
discrete lesions are often more resectable than invasive, lytic, and
VetBooks.ir lesions; the median PFS time for T1 tumors (<2 cm diameter) was ill-defined lesions. The use of esophagostomy or gastrostomy tubes
not reached and greater than 68 months compared with 28 months
may be necessary to provide supplemental nutrition in these cats
for T2 tumors (2–4 cm diameter) and 8 months for dogs with T3 for up to 4 months postoperatively. 90
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tumors (>4 cm diameter). Other favorable prognostic factors for RT alone is generally considered ineffective in the management
dogs receiving orthovoltage irradiation include rostral tumor loca- of cats with oral SCC. In nine cats treated with an accelerated radia-
tion, maxillary SCC, and young age. Rostral tumors (MST of 28 tion protocol (14 fractions of 3.5 Gy delivered twice daily for 9
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months compared with 2–10 months for caudal to extensive tumors), days), the overall MST was 86 days and, although not significant,
nonrecurrent tumors (MST 29 months compared with 7 months for the MST for cats with a complete response was 298 days. 100 The
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recurrent SCC), portal size less than 100 cm /m (MST 24 months combination of RT with radiation sensitizers or chemotherapy
2
compared with 7 months), and age less than 6 years (MST of 39 improves response rates and STs. Using the same accelerated radia-
months compared with 10 months) are good prognostic factors for tion protocol with carboplatin resulted in a 52% complete and
dogs treated with orthovoltage RT. Younger age is also prognostic 22% partial response rate at 30 days with a MST of 163 days in 31
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for dogs treated with megavoltage RT, as the MST of 315 days for cats. 101 Intratumoral etanidazole, a hypoxic cell sensitizer, resulted in
dogs with oral SCC and older than 9 years is significantly shorter than a 100% partial response rate in nine cats completing the RT course,
the 1080 day MST for dogs younger than 9 years. 81 with a median decrease in tumor size of 70% and a MST of 116
Chemotherapy is indicated for dogs with metastatic disease, dogs days. Gemcitabine was used at low doses as a radiation sensitizer
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with bulky disease, and when owners decline surgery and RT; how- in eight cats with oral SCC, with an overall response rate of 75%,
ever, although responses are noted in the macroscopic (gross disease) including two cats with complete responses, for a median duration
setting, durability of response is expected to be short (2–3 months). of 43 days and an MST of 112 days. However, gemcitabine is
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As the metastatic potential of oral SCC in dogs is relatively low, the not recommended as a radiosensitizer in cats because of significant
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role of adjuvant chemotherapy in minimizing the risk of metastatic hematologic and local tissue toxicities. The combination of RT
disease is unknown. In a series of 17 dogs treated with piroxicam with mitoxantrone holds some promise; in two series of 18 cats,
alone, the response rate was 17%, with one complete response and a complete response was observed in 73%, with a median dura-
two partial responses. The median PFI for dogs responding to tion of response of 138 to 170 days and an MST of 184 days. 97,107
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piroxicam was 180 days and significantly longer than the 102 days Tumor location, clinical stage, and the completeness of response are
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for dogs with stable disease. The outcome is better when piroxi- reported prognostic factors. 101,103 Location was a prognostic factor
cam is combined with either cisplatin or carboplatin. In a series of in this study, with significantly longer MSTs in cats with SCC of the
nine dogs treated with piroxicam and cisplatin, the overall MST was tonsils (not reached, mean 724 days) and cheek (not reached) than
237 days, with the 56% of dogs responding to this chemotherapy other locations. 101 A complete response at 30 days was also associ-
protocol having a significantly better MST (272 days) than nonre- ated with a significantly longer ST (379 days) than non- or partial
sponders (116 days). However, renal toxicity was reported in 41% responders (115 days). 101
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of dogs in this study and such toxicities limit the clinical usefulness Hypofractionated RT has also been reported in cats with oral
of this protocol. In another small series of seven dogs with T3 oral SCC. An overall response rate of 81%, with an MST of 174
SCC treated with piroxicam and carboplatin, a complete response days, was reported in 21 cats treated with an accelerated hypo-
was observed in 57% of dogs and this response was sustained in all fractionated RT protocol consisting of 10 daily fractions of 4.8
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dogs at the median follow-up time of 534 days. Novel therapies Gy for a total dose of 48 Gy. 103 In 54 cats treated with 8 to
under investigation include the combination of intralesional bleo- 10 Gy weekly fractions for a total dose of 24 Gy to 40 Gy, the
mycin and feline interleukin-12 (IL-12) DNA with translesional radiation-induced adverse effects were considered mild, with the
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electroporation. majority of owners reporting a subjectively improved quality of
life. 104 The overall MST was 92 days and cats with sublingual
Feline Oral Squamous Cell Carcinoma SCCs had a longer MST (135 days) than cats with mandibular
SCC (80 days). 104
The prognosis for cats with oral SCC is poor. There is no known Palliative stereotactic RT has been investigated in 20 cats with
effective treatment that consistently results in durable control or a 39% overall response rate and a median PFI and MST of 87 and
survival. Local control is the most challenging problem. In one 106 days, respectively; however, there was a high complication rate
series of 52 cats, the 1-year survival rate was less than 10%, with with mandibular fracture in 6 of 11 cats, fibrosis in three of six cats
MSTs of 3 months or less for surgery alone, surgery and RT, RT with lingual SCC, and oronasal fistula in one of three cats with
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and low-dose chemotherapy, or RT and hyperthermia. However, maxillary SCC. 105,106 In this study, cats with a low Bmi-1 percent-
42% of these cats had SCC involving the tongue, pharynx, or age, which is an oncogene responsible for suppression of cell-cycle
tonsils. In another series of 54 cats treated in general practice, the inhibitors and confers resistance to both chemotherapy and RT,
MST was 44 days, with a 10% 1-year survival rate. The oncologic had a significantly better outcome with longer median PFI than
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outcome may be better for cats with mandibular SCC. The MST cats with a higher Bmi-1 percentage. 106 Other prognostic factors
for seven cats treated with a combination of mandibulectomy and for cats with oral SCC treated with stereotactic RT include sex,
RT was 14 months, with a 1-year survival rate of 57%. Local tumor microvascular density, and degree of keratinization. 105
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recurrence was the cause of failure in 86% of these cats between 3 Localized irradiation with strontium-90 may be effective for
and 36 months after therapy. In another series of 22 cats treated selected cats with very superficial disease. 183
with mandibulectomy alone, the median DFI was 340 days. Chemotherapy appears to be largely ineffective in the manage-
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Tumor location and extent of resection had prognostic impor- ment of cats with oral SCC. No responses were observed in 18 cats
tance, with an MST of 911 days for rostral mandibulectomies, treated with liposome-encapsulated cisplatin or 13 cats treated