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Breast Cancer in Dogs

Cancer is a disease that affects many pets throughout their lifetime. Older female dogs are at a higher risk of developing breast cancer. Our Toledo vets share the symptoms and causes of breast cancer in dogs, the treatment options and what the outcome may be.

What is breast cancer in dogs?

Breast cancers in dogs are often referred to simply as mammary tumors. A mammary tumor develops due to abnormal replication of the cells that make up the breast tissue. Mammary tumors can be benign (non-cancerous) or malignant (cancerous). 

Breast cancer affects about one in four unspayed female dogs. Females spayed before their first estrus cycle reduce the chances from 25% to .05%. If spayed after their first heat but before the second, the risk of future breast cancer is approximately 8%. Half of the mammary tumors found in canines are benign, and of the half that are malignant, most can be successfully treated with surgery if caught early enough.

Breast cancer in canines is relatively common, occurring in approximately 25% of unspayed female dogs. Although it is rare, male dogs may also develop breast cancers. Breast cancer in males tends to metastasize aggressively.

What causes this cancer?

The exact causes of mammary tumors in dogs are not fully understood. However, it is well known that exposure to specific hormones, namely progesterone, increases the risk of developing mammary cancers in dogs. This is because progesterone stimulates growth factors (molecules that stimulate specific processes in the body) that cause mammary cells to multiply.

Although important in humans, hereditary factors have not been definitively linked to mammary cancer in dogs. Low-risk breeds include boxers and chihuahuas. High-risk breeds include poodles, English spaniels, English setters, and terriers. Early spaying has been shown to reduce the risk of mammary cancer dramatically.

Signs of Breast Cancer in Dogs

Most of the signs of breast cancer are related to the tumors themselves and are located on one of the eight to ten mammary glands present in most female canines. Most tumors are found near the mammary glands closest to the back legs. If you would like to see visual examples of breast cancer symptoms in dogs, you can search for pictures using your favorite search engine online.

When a dog develops breast cancer, the symptoms they may experience include:

  • Bloody discharge or pus from the nipple
  • Multiple bumps
  • Painful or swollen breasts
  • Singular lumps
  • Ulceration 
  • Yellow discharge or pus from the nipple

Systemic symptoms that might indicate cancer could include:

  • Breathing difficulties
  • Coughing
  • Lameness
  • Lethargy
  • Loss of appetite
  • Weakness
  • Weight loss
  • Enlarged lymph nodes

How To Diagnose Breast Cancer in Dogs

Your veterinarian will start your appointment by palpating the mass or masses and collecting data regarding their size, hardness, and mobility. They will also collect information about your dog’s health history, including applicable information about your animal’s last heat cycle, current medications, and pregnancies. X-rays and ultrasound may be used to visualize the spread but may not identify any microscopic dissemination of the cancer cells. 

A veterinary oncologist usually recommends a biopsy of any tumors and the lymph nodes. General testing is done to check for any concurrent disorders, and a complete blood count, urinalysis, and blood chemistry profile will be used to evaluate the patient's condition. This ensures the animal is healthy enough to undergo surgery and the required anesthesia. A biopsy of the tumor after surgical removal is usually necessary for a definitive diagnosis.

Treating Breast Cancer in Dogs

Surgery is by far the best treatment for dogs with solitary mammary tumors. If there is only one small mass and staging shows no evidence of spread, surgery may be the only treatment your dog receives.

For dogs with multiple tumors of one or both mammary chains, the associated–or all–of the mammary glands may need to be removed. If your dog is intact, an ovariohysterectomy (spay) is recommended and may be done at the same time as the mammary gland removal.

For dogs with larger tumors or evidence of spread to other areas of the body, chemotherapy is typically recommended. There is increasing evidence that radiation therapy may provide some benefit for dogs with inflammatory carcinomas in addition to chemotherapy. Your veterinarian will discuss the best options for your dog’s particular situation.

Recovery After Breast Cancer Surgery

While specific timelines can vary, many dogs are released one to five days post-op. Your vet will provide you with instructions for caring for your dog during its recovery. It is important to follow these instructions to ensure proper healing.

Caring for your dog after surgery can include:

  • Elizabethan (e-collar) collar for 10–14 days after surgery to prevent your dog from licking or chewing the wound
  • Restricted activity for about two weeks while the incision heals
  • Keeping bandages clean and dry during the healing process

Life Expectancy for Dogs With Breast Cancer

Dogs with breast cancer generally have a life expectancy of one or more years with early treatment of the disease. They generally have a good quality of life with successful treatment.

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. Please note that Shoreland Animal Hospital does not offer oncology services.

If your dog has developed any unexplained lumps, bumps or other symptoms, please contact our vets for an examination. 

Welcoming New Patients

Shoreland Animal Hospital is accepting new patients! Our veterinary team is passionate about the health of Toledo pets and is looking forward to meeting you and your furry friend. Contact us today to schedule an appointment!

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