Page 463 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 23 Cancer of the Gastrointestinal Tract 441

TABLE 23.5 Prognostic Factors for Dogs with Oral Malignant Melanoma Treated with Surgery, with or without
Radiation Therapy, Chemotherapy, and/or Immunotherapy
VetBooks.ir Prognostic Factor Median Progression-Free Survival Median Survival Time
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Age
630 days if <12 years
—
224 days if ≥12 years
Tumor size 56 — 511 days if >2 cm
164 days if >2 cm
Tumor size 40 — 630 days if <2 cm
240 days if 2–4 cm
173 days if >4 cm
Tumor size 41 >567 days if <3 cm 874 days if <3 cm
245 days if >3 cm 396 days if >3 cm
Metastasis at diagnosis 41 567 days if no metastasis 818 days if no metastasis
187 days if metastasis 131 days if metastasis
Clinical stage 40,41 >567 days for stage I 874 days for stage I
>187 days for stage II 818 days for stage II
245 days for stage III 207 days for stage III
PDGFRs-α and -β coexpression 30 239 days if no coexpression 335 days if no coexpression
159 days if no coexpression 183 days if no coexpression
Ki67 30 484 days if Ki67 <19.5% 484 days if Ki67 <19.5%
188 days if Ki67 >19.5% 224 days if Ki67 >19.5%
PDGFR, Platelet-derived growth factor receptor.

considerably from 150 to 874 days with 1-year survival rates less time to local recurrence of 139 days. 44–49 In one study progressive
than 35%. 9,13–24,30–68 In a recent study, the median progression- local disease was observed in all dogs that did not achieve a complete
free interval (PFI) and MST after surgery alone for oral MM were response. The most common cause of death is metastasis, and this
44
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greater than 567 days and 874 days, respectively. Variables which is reported in 58% of dogs with a median time of metastasis of 311
46
are known to have prognostic significance in dogs treated with days. The MST for dogs treated with RT is 192 to 401 days, with
surgery alone or in combination with other modalities include a 1-year survival rate of 36% to 48% and a 2-year survival rate of
age, tumor size, clinical stage, the ability of the first treatment 21%. 44–49 Local tumor control and ST are significantly improved
to achieve local control, and histologic and immunohistochemi- with rostral tumor location, smaller tumor volume, no radiographic
cal criteria such as the degree of differentiation, mitotic index, evidence of bone lysis, postoperative irradiation of microscopic dis-
nuclear atypia score, pigment quantification, COX-2 expression, ease, and megavoltage irradiation. 43,45,47,48 In one series of 140 dogs
PDGFR expression, Ki67 expression, and c-kit expression (Table with oral MM, the MST was 21 months if none of these risk factors
23.5). 9,13–24,30–68 In some studies, tumor location has prognos- were present compared with an MST of 11 months with one risk
tic importance with rostral mandibular and caudal maxillary sites factor, 5 months with two risk factors, and three months with all
having a better prognosis than other sites. 32,37,53 MSTs are signifi- three risk factors. 47
cantly shorter for dogs with recurrent oral MM compared with Tumor size is important with median PFS for dogs with T1
dogs with previously untreated oral MM. In one study, dogs oral melanomas of 19 months compared with less than 7 months
31
43
treated with adjunctive RT had significantly longer STs, but this for T2 and T3 tumors. In one study of 111 dogs treated with
result may have been confounded by age, which was also prognos- either orthovoltage or megavoltage hypofractionated protocols,
40
tic in this study. In 64 dogs with surgically treated well-differ- tumor size and clinical stage had a significant effect on outcome
entiated melanomas of the lips and oral cavity, 95% of dogs were with MSTs for dogs with stage I, II, III, and IV oral malignant
either alive or had died of unrelated causes at the end of the study melanoma of 758, 278, 163, and 80 days, respectively. In this
48
period. Prognostic information for melanocytic tumors in dogs study, there was a greater risk of death and decreased STs overall
69
has recently been reviewed. 39 (MSTs of 233 days compared with 122 days) and for dogs with
Oral melanoma is responsive to hypofractionated RT protocols. stage III melanoma (MSTs of 210 days compared with 99 days)
48
A number of different hypofractionated RT protocols have been when treated with orthovoltage rather than megavoltage RT.
described: (1) 3 weekly 8 to 10 Gy fractions for a total dose of 24 The median PFI was significantly prolonged in one study of 27
to 30 Gy, 44,47 (2) 4 weekly fractions of 9 Gy for a total dose of 36 dogs when hypofractionated RT was combined with adjuvant
Gy, 45,47 (3) 6 weekly 6 Gy fractions for a total dose of 36 Gy, (4) 5 oral temozolomide compared with hypofractionated RT alone.
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49
49
fractions of 6 Gy over 2.5 weeks, and (5) 8 weekly 6 Gy fractions Hypofractionated RT has also been described in five cats with oral
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for a total dose of 48 Gy. Response rates are excellent, with 81% melanoma, resulting in a 60% response rate and MST of 146 days
to 100% of tumors responding and a complete response observed in (range: 66–224 days). 29
up to 70% of melanomas. 42–49 Local recurrence is reported in 15% Effective systemic adjuvant therapies (e.g., immunotherapy,
to 26% of dogs experiencing a complete response with a median chemotherapy) are ultimately necessary for successful management