Page 640 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

618 PART IV Specific Malignancies in the Small Animal Patient

Recently a novel grading system for feline MGTs has been Age
proposed which includes lymphovascular invasion (see Table The results regarding age and prognosis are conflicting. Several
studies report that older cats have a worse prognosis; however, bias
A limitation of this system is that when evaluating
218
28.4b).
VetBooks.ir histologic section(s) of a tumor, lymphovascular invasion might due to differences in treatments or differences in tumor size and
not be present in the selected section(s). Standardization of this
clinical stage may exist. Importantly, a prospective randomized
method would be improved by additional information, such as trial found no difference according to age when comparing cats
number of sections, and trimming procedure. Pathologists might that were younger or older than 10 years. 220
then consider including both systems in their report to allow a
comparison and a more robust assessment of its prognostic value. Therapy
Using this grading system, the median OST of cats with grade
I tumors was 31 months (36 months with the Elston and Ellis– Surgical Treatment
based scoring system), grade II tumors was 14 months (18 months The surgical dose recommended for treating feline MGTs is much
with the Elston and Ellis–based scoring system), and grade III clearer than in the dog. A chain mastectomy (unilateral for cats
tumors was 8 months (6 months with the Elston and Ellis–based possessing a single tumor or a staged bilateral chain mastectomy
scoring system). 218 for cats with bilateral tumors) resulted in a statistically significant
improvement in DFI and ST, as opposed to cats receiving conser-
Clinical Prognostic Factors vative tumor excision in a series of 100 cats. 219 In a retrospective
case series of 53 cats, although no significant difference was found
Few studies reporting prognostic factors in cats with MGTs are between the type of surgical procedure performed, cats experienced
prospective, only one is randomized, and most are underpowered longer DFIs after either unilateral or bilateral chain mastectomies
or not stratified according to treatment. Therefore the results vary compared with partial mastectomy. 177 Recently, a multiinstitu-
and may be significantly affected by bias. Tumor size has, however, tional retrospective case series of 107 cats having either unilateral
consistently been reported to have prognostic significance, includ- mastectomy or bilateral mastectomy for mammary adenocarci-
ing the results of two large prospective studies. noma found a longer median progression-free ST of 542 days for
cats treated with bilateral mastectomies versus 289 days for cats
Tumor Size treated with unilateral mastectomy. 222 In the multivariable analy-
Three size categories have shown prognostic significance: (1) sis, disease-specific death was greater for those cats treated with
3
smaller than 8 cm or smaller than 2 cm diameter; (2) 8 to 27 a unilateral mastectomy and those that developed metastasis. 222
cm or 2 to 3 cm diameter; and (3) larger than 27 cm or larger In addition, the disease-specific ST was statistically improved for
3
3
than 3 cm diameter. Cats with small (<2 cm) tumors can be cats treated with both mastectomy and adjuvant chemotherapy. 222
effectively treated with surgery alone, specifically radical mas- In a multiinstitutional retrospective case series comparing patients
tectomy, with a MST of more than 3 years, whereas cats with treated with surgery versus surgery and adjuvant DOX-based che-
tumors larger than 3 cm have a MST of only 6 months according motherapy, the subset of cats having unilateral mastectomies fol-
to a large retrospective study. 219 Cats with 2- to 3-cm diameter lowed with chemotherapy had significantly longer MSTs than cats
tumors survived an average of 2 years. Several other publications having unilateral mastectomies without chemotherapy (1998 vs
have confirmed this association between survival and tumor 414 days). 201 In that series, local recurrence developed in 50%
size. 175,177,199,220,221 of cats and, although not statistically significant, also appears to
support the use of bilateral mastectomies for feline mammary car-
Lymph Node Status cinomas. 201 In a report of male cats diagnosed with mammary car-
Surprisingly few studies have evaluated LN status and its prognos- cinomas, a trend toward more frequent local recurrence correlated
tic significance in cats with MGTs. In a large prospective study of with more conservative resections. 184 Thus, for cats, a unilateral
202 cats, those with LN metastasis had significantly shorter STs or staged bilateral chain mastectomy is recommended for cura-
than cats with negative LNs. 199 A retrospective study with 92 cats tive-intent treatment of mammary carcinoma. For some cats with
supported these findings; all cats with LN metastasis died within excessively loose mammary tissue, a bilateral chain mastectomy
the first 9 months of diagnosis. 217 A retrospective study of 107 cats can be performed during a single surgical session if minimal post-
treated with either unilateral mastectomy or bilateral mastectomy surgical tension can be achieved, but these cats can have a more
for mammary adenocarcinomas revealed that LN metastasis at the difficult recovery with increased complication rates (Fig. 28.6). 222
time of mastectomy had a significant negative association with For tumors that are fixed, muscular fascia or portions of the body
progression-free ST and an increased risk of death, but a third of wall should be included with en bloc resections. In a retrospective
cats having histologic evidence of LN metastasis did not progress case series, bilateral mastectomy in cats with LN metastasis was
to additional metastasis. 222 found to be protective against disease progression on multivariable
study analysis. 222 Thus bilateral mastectomy is recommended for
Breed MGTs in cats.
Domestic shorthair cats had significantly better outcomes than The high malignancy rate of mammary carcinoma and the
purebred cats in a prospective randomized trial of cats with mam- poor prognosis associated with LN metastasis supports aggres-
mary carcinomas. 220 Another study reported that Siamese cats sive LN assessment. This could include ultrasound-guided FNA
had a worse prognosis than domestic shorthairs. 223 These studies of difficult to palpate LNs and inguinal lymphadenectomy con-
may in fact complement each other; however, the first study did current with chain mastectomy. Sentinel LN mapping has been
not provide information regarding how many Siamese cats were described in the cat and was the original model for the proce-
included in the purebred group. Several other studies have not dure, which is common for human breast cancer patients. 111,115
found breed to be prognostic when adjusted for other factors. Published techniques in the cat include CT evaluation after