Mammary Gland Tumors in Dogs
BASICS
DEFINITIONBenign or malignant tumors of the mammary glands
Pathophysiology
- Dogs spayed before first estrous cycle have 0.5% risk compared with intact bitch.
- Dogs spayed before second estrous cycle have 8.0% risk compared with intact bitch.
- Dogs spayed after second estrus have 26% risk compared with intact bitch.
- Dogs spayed after 2.5 years of age--no sparing effect on risk.
Incidence/Prevalence
- 198.8/100,00 female dogs
- about 50% are malignant
- Almost exclusively affects females
- About 50% of patients have multiple tumors
Mean Age and Range
- Median age about 10.5 years (range, 1-15 years)
- Uncommon in dogs < 5 years
- Thoracic radiography to detect metastasis
- Abdominal radiography to detect metastasis to iliac (sublumbar) lymph nodes
Histopathologic Findings
- 50% benign
- 42% adenocarcinoma
- 4% inflammatory carcinoma
- 4% sarcoma
TREATMENT
- Surgery the primary mode of treatment
- Chemotherapy infrequently reported
CLIENT EDUCATION
- Never leave a mammary lump in place and observe.
- Early surgical intervention is best.
- Advise spaying before first estrus.
SURGICAL CONSIDERATIONS
- Local excision (ie, simple, regional , or unilateral mastectomy) with wide and deep margins (at least 2 cm in all directions) can be as effective in terms of disease free interval as radical bilateral mastectomy.
- Chemotherapy is infrequently reported, but it may be effective in some patients.
