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Breast tumors in dogs

Mammary tumors are the most common tumors in unspayed female dogs. They appear as one or more lumps along the mammary chains, from the armpit to the groin. Some of them are benign, another part are cancerous, and it is impossible to disting...

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Definition Signs Causes Diagnosis Treatment Prevention Complications When to see a vet Prognosis FAQ Sources Affected species

What is it?

Mammary tumors are the most common tumors in unspayed female dogs.

They appear as one or more lumps along the mammary chains, from the armpit to the groin.

Some of them are benign, another part are cancerous, and it is impossible to distinguish them by touch: only laboratory analysis can decide.

Key point

A lump on the udder is not synonymous with cancer: a significant proportion of these masses are benign. But none can be classified without analysis, and the smaller it is removed, the simpler the intervention.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Related signs — each one links to its page:

Nodules under the skin Swollen udder Swelling Pain Scabs and skin lesions Weight loss Swollen lymph nodes

One or more firm lumps along a mammary chain, often discovered by stroking the female dog's belly.

Masses of variable size, sometimes multiple and on both chains.

Increase in volume of a udder, with or without discharge from the teat.

Ulceration of the skin above the mass, crusting, bleeding, unpleasant odor.

Significant redness, heat and pain of several breasts at the same time, in a particular and severe form which resembles an infection.

Weight loss, fatigue and shortness of breath in advanced forms.

When to consult without delay

This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.

Causes and risk factors

The development of these tumors is strongly linked to female sex hormones, which stimulate the mammary gland with each cycle.

The more times a dog has been in heat, the more the mammary tissue has been stressed and the risk increases.

The use of hormonal treatments, particularly those which suppress heat, is a recognized risk factor.

A hereditary component is likely in certain lines.

Absence of sterilization, or sterilization carried out late in the dog's life.

Age: Frequency increases markedly in middle to older aged female dogs.

Repeated contraceptive hormonal treatments.

Overweight and obesity, especially during the growth period.

Certain breeds are more affected, including the Poodle, Dachshund, Spaniel, Yorkshire and Setter.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

The veterinarian methodically palpates both mammary chains as well as the lymph nodes in the armpit and groin, and notes the size and location of each mass.

A fine needle aspiration can provide guidance, but it does not replace the analysis of the removed mass: it is histology which gives the definitive diagnosis.

Chest x-rays are taken before surgery because these tumors can spread to the lungs.

An ultrasound of the abdomen and a blood test complete the evaluation, particularly in older dogs.

Treatment

Surgery is the main treatment. Depending on the number, size and position of the masses, the veterinarian removes the mass alone, part of the mammary chain or the entire chain, with the lymph nodes involved.

All masses removed are sent to the laboratory: the report indicates whether they were benign or malignant, and whether the removal was complete.

Sterilization can be proposed during the same operating time; its benefit on already established tumors is debated, but it eliminates the risk of other diseases of the uterus and ovaries.

Chemotherapy is considered for certain aggressive or already extensive forms.

Pain management always accompanies the procedure and the return home.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

This is where prevention is the most effective of all dog cancers: sterilization before the first heat period considerably reduces the risk of mammary tumors.

The benefit diminishes as the dog goes through cycles, but later sterilization remains of interest for other health reasons.

Avoid hormonal treatments intended to suppress heat, unless specifically indicated by a veterinarian.

Maintain a healthy weight, especially in young dogs.

Pass your hand over the udders once a month: they are easy to examine and a lump is detected early.

Possible complications

Ulceration and superinfection of the masses, sources of pain and bad odor.

Diffusion to neighboring lymph nodes, then to the lungs.

Recurrence in the same place or appearance of new masses on the other udders.

Inflammatory form, rare but severe, where the udder is red, hot and very painful, often initially confused with an infection.

When to see a veterinarian

You feel a lump, even a small one, along your dog's udders.

A known mass grows, hardens or multiplies.

The skin over a mass is ulcerated, bleeds, or oozes.

Several udders become red, hot and painful in a short time: consult quickly.

Your dog is out of breath, coughing or losing weight while she has breast masses.

Prognosis

The prognosis depends on the benign or malignant nature of the mass, its size at the time of the operation, lymph node involvement and the precise type identified in the laboratory.

A benign mass removed is permanently resolved, and many female dogs are in this situation.

A malignant tumor removed while it is still small and localized offers significantly better prospects than a large or ulcerated mass: the size at the time of diagnosis is one of the most determining elements, which justifies not waiting.

Frequently asked questions

My dog has a small lump on her udder, should we be worried?

You need to have it examined, without panicking. Some of these masses are benign. The important point is not to monitor it for months: a small mass is easily removed, a large mass complicates the operation and darkens the prognosis.

Does sterilization really protect?

Yes, and it is one of the best established effects in pet medicine. Sterilizing before the first heat period greatly reduces the risk of mammary tumors. The benefit diminishes with each additional cycle, but sterilization maintains other health benefits at any age.

Should all the udders be removed?

Not systematically. The extent of the surgery is decided on a case-by-case basis, depending on the number of masses, their position and the general condition of the female dog. The veterinarian seeks the balance between removing enough tissue and limiting the burden of the procedure.

My dog had a nervous pregnancy, is this related?

Nervous pregnancies demonstrate a strong hormonal impregnation, the same terrain that favors breast tumors. They do not directly cause cancer, but they warrant discussing the question of sterilization with your veterinarian.