What are mammary tumours in female dogs?

Neoplasms arising from the mammary glands. They are the most common tumour in intact female dogs — representing 25-50 % of all tumours in female dogs. Approximately 50 % are malignant.

How do I detect a mammary tumour in my dog?

By regularly palpating the mammary chain (5 pairs of glands from the chest to the groin). Look for nodules, lumps or thickening, nipple discharge, ulceration or fixation to the skin.

Does spaying protect against mammary tumours?

Yes, significantly. If the dog is spayed before the first season, the risk is 0.5 %. After the first season it rises to 8 %, and after the second to 26 %. Early spaying is the best prevention.

How are mammary tumours treated in dogs?

Surgery (mastectomy) is the treatment of choice — tumour removal with clean margins, and depending on the type, adjacent glands or the entire chain. Prognosis depends on histological type, grade and whether metastasis is present.

Dog Mammary Tumour: Signs, Types and Treatment

Why Are They So Common?

Mammary tumours are the most common neoplasm in intact female dogs, representing 25-50 % of all tumours in females. The incidence is 3 times higher in dogs than in women and 100 times higher than in cats. Chronic hormonal stimulation by oestrogens and progesterone (with each season) is the main risk factor.

Early Detection: Self-Examination

The female dog has 5 pairs of mammary glands: cranial thoracic, caudal thoracic, cranial abdominal, caudal abdominal and inguinal. The most commonly affected are the 4th and 5th pairs (the most hormonally active).

How to palpate: with the dog lying on her back, run your fingers along the entire mammary chain every 1-2 months. Look for:

Solid or cystic nodules of any size.
Changes in consistency or size.
Nipple discharge.
Ulceration or fixation to skin or muscle.
Diffuse inflammation of the entire gland (may be confused with mastitis).

Types and Prognosis

Approximately 50 % of canine mammary tumours are malignant:

Simple adenoma/fibroadenoma: benign — excellent prognosis after removal.
Tubular or papillary carcinoma: malignant but low metastatic potential — good prognosis with clean surgery.
Inflammatory carcinoma: the most aggressive — diffuse, hot, painful, very poor prognosis.
Carcinosarcoma: poor prognosis.

Treatment

Surgery: the primary treatment. Options range from simple nodule excision to unilateral or bilateral mastectomy, depending on the number and distribution of tumours.
Chemotherapy: used in high-grade carcinomas or with metastases (doxorubicin, cyclophosphamide).
Simultaneous spaying: recommended in the same surgery — reduces recurrence risk and prevents future tumours.

Prevention

Spaying before the first season reduces mammary tumour risk to 0.5 % compared to 26 % in intact dogs. This is one of the strongest evidence-backed reasons to recommend early spaying.