Page 1384 - Clinical Small Animal Internal Medicine

1322 Section 11 Oncologic Disease

nodes is imperative. Some studies have found that the Forty to fifty percent of canine mammary masses are
VetBooks.ir two caudal mammary glands are more commonly benign. Both benign and malignant tumors may be sim-
ple or complex. Simple tumors are composed of only one
affected.
Inflammatory mammary carcinomas account for
approximately 8% of mammary masses. Dogs are often cell type whereas complex masses have both luminal and
myoepithelial components. In complex carcinomas, the
systemically ill, with painful, edematous mammary epithelial cells are neoplastic while the myoepithelium is
glands. Dogs may also be inappetent, lethargic, and benign.
febrile. Inflammatory mammary carcinomas may be mis- The most common benign masses include ductal ecta-
diagnosed as mastitis, severe dermatitis or vasculitis. sia, lobular and fibroepithelial hyperplasia, adenomatous
masses, and benign mixed tumors. Most malignant
tumors are carcinomas. Simple mammary carcinomas
Diagnosis
are most often tubular, tubulopapillary, cystic, papillary,
Evaluation of the mammary chain should be part of a cribriform or solid. Mucinous carcinoma, squamous cell
routine examination. The size, mobility, and appearance carcinoma, and malignant mixed tumors are less com-
may increase suspicion for malignancy. A minimum mon. A histopathologic grading system for mammary
database, including complete blood count, chemistry carcinomas exists, and has been found to be prognostic
profile, urinalysis, and thoracic radiographs, should be in several studies. Criteria include the extent of tubule
completed. An abdominal ultrasound to assess visceral formation, nuclear pleomorphism, and mitotic rate.
lymph nodes is indicated and regional lymph nodes Mammary sarcomas are also reported, with extraskeletal
should be aspirated when possible. The lymphatic drain- osteosarcoma being most common.
age is unpredictable, but axillary, sternal, and inguinal
lymph nodes should be assessed. Therapy
Tumor stage has important prognostic and treatment
implications, and most clinicians use a modified five‐tier Surgery is an integral part of therapy for mammary
World Health Organization (WHO) tumor, node, metas- tumors, with the exception of inflammatory carcinomas
tasis (TNM) staging scheme (Table 149.1). The original and those with widespread metastases. In dogs, it is
WHO staging scheme has four stages. Tumor size has unclear whether the extent of surgery is prognostic.
been found to be prognostic, and so this delineates the Most studies suggest that for a single mass, the outcome
first three stages. The presence of lymph node metasta- is the same for mass resection and radical mastectomy as
ses determines stage 4 disease regardless of tumor size, long as excision is complete. However, given the preva-
and dogs with distant metastases have stage 5 disease. lence of multiple tumors, unilateral radical mastectomy
Surgical resection and histopathology provide a has also been advocated. In a 2008 study, 58% of dogs
definitive diagnosis in most cases. Cytology can be per- developed a second tumor which would have been pre-
formed if presurgical diagnosis is desired. Cytology has vented by unilateral mastectomy. However, in the same
been reported to be 67.5–93% accurate at differentiat- study, had all dogs received unilateral mastectomies, 42%
ing benign from malignant masses, with sensitivity of would have had unnecessarily aggressive surgeries. If
86–96% and 88–100% specificity for malignancy. multiple mammary masses are present, a regional, uni-
Cytologic diagnosis of malignancy also correlated well lateral or staged bilateral mastectomy is indicated.
with survival. One study found that ovariohysterectomy at the time
of mass resection or within two years of developing
mammary carcinoma improved two‐year survival. This
Table 149.1 Canine mammary tumor staging. Modified World may be because tumors in intact females retain some
Health Organization Tumor, Node, Metastasis (TNM) staging
scheme hormone responsiveness. Hormone therapy with agents
like tamoxifen (estrogen receptor blocker) is not com-
monplace, in part because of the ease of sterilization and
Lymph node Distant
Stage Tumor size metastasis metastasis also because of the significant risk of pyometra in intact
females. If the dog is to be spayed at the time of mass
1 T1 (T <3 cm) N0 (none) M0 (none) removal, ovariohysterectomy should be performed first
2 T2 (T N0 (none) M0 (none) to avoid tumor seeding.
3–5 cm) For large, high‐grade, or metastatic tumors, surgery
3 T3 (T >5 cm) N0 (none) M0 (none) alone is unlikely to be curative. However, the role of
4 Any T N1 (positive) M0 (none) chemotherapy for canine mammary carcinoma is
5 Any T Any N M1 (positive) unclear. Adequately powered, randomized, controlled
trials are lacking. Chemotherapy is often recommended