Page 639 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 28 Tumors of the Mammary Gland 617

the remaining MGs is important when evaluating a cat with TABLE 28.7 Staging of Feline Mammary Tumors 201
a prior history of MGTs, especially if treated with local mas- Lymph Node
tectomy, because new primary tumors are common. Tumor(s)
VetBooks.ir size at diagnosis depends on how early it is detected and how Stage Tumor Size Status Metastasis
aggressive the tumor behaves. Larger tumors may become
ulcerated, inflamed, and infected. Local LNs may or may not Stage I T 1 <2 cm N 0 M 0
appear enlarged. Inflammatory mammary carcinomas are rare Stage II T 2 2–3 cm N 0 M 0
in cats and the clinical picture and outcome are similar to those Stage III N 1 (positive)
described in the dog. 200 T 1 or T 2 N 0 or N 1 M 0
T 3 >3 cm
M 0
Clinical Assessment, Diagnosis, Workup, and Stage IV Any Any M 1
Clinical Staging From McNeill CJ, Sorenmo KU, Shofer FS, et al.: Evaluation of adjuvant doxorubicin-based
chemotherapy for the treatment of feline mam mary carcinoma, J Vet Intern Med 23:123–129,
Cats with mammary masses tend to be older and their tumors 2009.
are commonly malignant; therefore a thorough workup is recom-
mended to ascertain any comorbidity and advanced disease. This
may include CBC, serum biochemistry, serum T concentration, fibroadenomatous change. 209 Fibroadenomatous change (fibroep-
4
three-view thoracic radiographs, abdominal ultrasound, and uri- ithelial hyperplasia, fibroepithelial hypertrophy, mammary hyper-
nalysis, in addition to FNA of any mammary masses and any pal- trophy) is common in the cat, usually affects several glands, and
pable (including normal-sized) regional LNs. is characterized by the proliferation of interlobular ducts, tubules,
and periductal stromal cells. The stroma is often edematous or
Staging System myxomatous, and both the epithelial and stromal cell nuclei
Feline MGTs are staged similar to canine tumors using a modi- exhibit some pleomorphism with mitoses. This lesion is hormon-
fication of the original system published by Owen. 124,201 In the ally induced and occurs in progestin-treated female and male cats,
modified system, stage advances from I to II to III as the size as well as being associated with pregnancy. Most cases regress at
increases from smaller than 2 cm, to between 2 and 3 cm, to the end of pregnancy or cessation of progestin treatment. 128,202
larger than 3 cm. 125 Unlike the canine system, stage III disease
also includes T1 or T2 tumors with concurrent LN metastasis Benign Feline Mammary Neoplasms
and LN metastasis does not need to be present with T3 tumors.
Stage IV disease is any tumor with any LN metastasis and distant Benign tumors in cats are uncommon and include simple ade-
metastasis. 201 This staging system should not be used with MG noma, ductal adenoma, fibroadenoma, and intraductal papillary
sarcomas (see Table 28.6). adenoma (duct papilloma). 128,202

Histopathology
The vast majority of feline MGTs are malignant (85%–95%) Malignant Mammary Neoplasms
with an aggressive biologic behavior, and lymphatic invasion and The predominant malignant tumor types in cats are simple
LN metastasis are more common at the time of initial diagnosis and epithelial in origin and as such represent carcinomas of
than in dogs. Early classifications of feline MGTs were simpler various types. Tubular carcinomas, tubulopapillary carcino-
than that used for canine tumors. 128 Complex and mixed tumors mas, and solid carcinomas are most common. Other vari-
showing the same features of the canine counterparts have not ants include cystic-papillary carcinoma, cribriform carcinoma
been diagnosed in the feline MG; however, new and previously (when tubules are nearly undetectable), micropapillary inva-
unclassified subtypes have been reported. 202 Morphologic features sive carcinoma, comedocarcinoma, anaplastic carcinoma,
of each subtype are identical to the canine counterparts and, as intraductal papillary carcinoma, ductal carcinoma, and, less
per dogs, the predominant morphologic pattern is used to classify commonly, squamous cell carcinoma, mucinous carcinoma,
the tumor. lipid-rich carcinoma, adenosquamous carcinoma, and spindle
Similar to dogs, a molecular approach to MGT classification cell carcinoma. 128,197,200,202,209–216
has been attempted in cats. 203–208 Despite lack of standardized
methods and variability of results, mammary carcinomas in cats Histopathologic Prognostic Factors and Grading
were associated with the highest percentage of triple-negative
(HR– and HER-2–) MGTs, associated with frequent expression Grading was initially thought not to be prognostic in cats;
of both basal cytokeratins and vimentin, and had the worst prog- therefore the classification of mammary tumors was based
nosis. This seems to suggest that the cat may be a suitable model on morphologic criteria only. More recently, histologic grad-
for some subtypes of human BC, such as the HR-independent ing using a system similar to that in dogs (see Tables 28.3
basal-like cancers. and 28.4a) has been shown to be prognostic in cats. 210,217
In addition to histologic grade, lymphovascular invasion and
Hyperplasia and Dysplasia LN metastasis are independent prognostic factors. 210,217 Thus
the histopathologic criteria used in dogs (i.e., grade, vascular
The various hyperplastic and dysplastic lesions seen in cats invasion, LN status) can be used in cats when assessing risk
include duct ectasia, lobular hyperplasia (regular, with secretory for metastasis and prognosis, and should be incorporated into
[lactational] activity, with fibrosis [interlobular fibrous connec- decisions regarding the need for systemic treatment in cats
tive tissue], and with atypia), epitheliosis, papillomatosis, and with MGTs (Table 28.7).