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Mammary Gland Neoplasia, Dog 623

• Regular examination of the mammary SUGGESTED READING AUTHOR: Erin K. Malone, DVM, DACVIM
chain De Campos CB, et al. Use of surgery and carboplatin EDITOR: Kenneth M. Rassnick, DVM, DACVIM
VetBooks.ir tion when abnormalities are found with advanced clinical staging. In Vivo 28:863-866, Diseases and Disorders
• Prompt presentation for veterinary examina-
in feline malignant mammary gland neoplasms
2014.

Mammary Gland Neoplasia, Dog Client Education
Sheet

BASIC INFORMATION ○ TP53 ○ Regional lymph node: N0, no metastasis;
○ ERBB2 (HER2/NEU) N1, metastasis detected
Definition ○ BCRA1, BCRA2 ○ Distant metastasis: M0, no metastasis;
Mammary gland tumors are benign or malig- M1, metastasis detected
nant neoplasms arising from mammary tissue. RISK FACTORS
• Timing of OHE affects the relative risk of
Synonyms developing mammary gland tumors.
• Mammary or breast cancer/tumor ○ 0.5% of the risk of an intact bitch if OHE Stage Grouping T N M
• Benign mammary tumors: adenoma/ is performed before the first estrus
cystadenoma, benign mixed mammary ○ 8% of the risk of an intact bitch if OHE I T1 N0 M0
tumor, duct papilloma, myoepithelioma, is performed between the first and second II T2 N0 M0
complex adenoma, fibroadenoma estrus III T3 N0 M0
• Malignant mammary tumors: carcinoma in ○ 26% of the risk of an intact bitch if OHE IV T1-3 N1 M0
situ, simple carcinoma (tubular/tubulopapillary, is performed between the second and third
solid, cribriform, and anaplastic), complex car- estrus V T1-3 N0, N1 M1
cinoma, inflammatory carcinoma (uncommon), • Females spayed after 2 years of age have
carcinosarcoma (rare), sarcomas (fibrosarcoma, a sevenfold greater risk of mammary
osteosarcoma, other; uncommon) neoplasia than those spayed before age
• Different pathologic classification schemes 6 months. • Histologic staging
exist. • Body condition/diet: reduced risk (odds ratio ○ 0: carcinoma in situ
= 0.04) in dogs with lean body condition at ○ 1: stromal invasion
Epidemiology age 9-12 months ○ 2: vascular/lymphatic invasion; lymph
SPECIES, AGE, SEX • Hormone therapy: progesterone and/or node metastasis
• Mammary gland tumors are common tumors estrogen administration may lead to a greater ○ 3: distant metastases
in female dogs, and the most common tumor than twofold increase in the risk of benign • Histologic grading of carcinomas is based
in intact female dogs. and malignant mammary tumors. on tubule formation, nuclear pleomorphism,
○ Incidence ≈2:1000 • Pregnancy, lactation, pseudocyesis and mitotic index and offers prognostic
○ Due to the common practice of early-age ○ Unlike in people, pregnancy does not significance. Low-, intermediate-, and high-
ovariohysterectomy (OHE), the incidence afford a protective effect against the grade tumors correspond to well, moderately,
has decreased in the United States. In development of mammary tumors in dogs. and poorly differentiated tumors.
European countries, mammary tumors Lactation and pseudocyesis also do not
represent 40%-70% of all tumors in seem to have an influence. HISTORY, CHIEF COMPLAINT
female dogs. • Owners may notice a swelling, lump, or
• Mammary tumors affect middle-aged to older ASSOCIATED DISORDERS ulceration in their dog’s mammary chain,
dogs; median age for malignant tumors is • Ovarian cysts, cystic endometrial hyperplasia or it may be an incidental finding on routine
10-11 years. • Mammary tumors in male dogs may be physical exam.
• Mammary gland tumors in male dogs are associated with hormonal disturbances (e.g., • Duration of clinical signs is highly variable,
uncommon (≈1% of mammary tumors occur estrogen-secreting testicular Sertoli cell tumor). ranging from days to months.
in males). • Up to 21% of dogs with inflammatory • With metastasis or inflammatory carcinoma,
carcinoma may have concurrent disseminated dogs may be presented due to general signs
GENETICS, BREED PREDISPOSITION intravascular coagulation (DIC), and appro- of illness or specific complaints attributable
• Breeds at increased risk priate testing should be assessed accordingly to a certain site of metastasis (e.g., lameness
○ Spaniel breeds (p. 269). in cases of bone metastasis, cough due to
○ Pointer breeds • Secondary inflammatory carcinoma may pulmonary metastasis).
○ Poodles develop after (mean, 48 days) surgical removal
○ Dachshunds of a mammary tumor; secondary inflamma- PHYSICAL EXAM FINDINGS
○ German shepherds tory carcinoma typically behaves as aggressively • Varies, depending on extent and stage of the
○ Yorkshire terriers as primary inflammatory carcinoma. disease
• There seems to be a genetic factor in the Clinical Presentation • Single or multiple nodules may be present.
development of mammary tumors, but a Multiple tumors are common in dogs, and
specific, common mutation has not been DISEASE FORMS/SUBTYPES both mammary chains may be affected. The
identified. The following genes have been • Clinical staging caudal glands are affected most frequently.
found to be mutated in selected canine ○ Tumor: T1 < 3 cm; T2 3-5 cm; T3 > Multiple tumor types among different glands
mammary gland tumors (p. 621): 5 cm are common.

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