MAMMARY GLAND NEOPLASIA

About the Diagnosis

Cause: Dogs and cats of both sexes have breast tissue that lies as two series or "chains" of mammary glands along the midline of the belly and chest, with a nipple for each of the ten mammary glands. Like in people, it is possible for tumors to develop within these mammary glands in dogs and cats. These tumors may be benign (harmless) or malignant (cancerous).

The vast majority of mammary tumors that occur in dogs occur in females (99%) versus in males (1%), and mammary tumors are the most common tumor of female dogs. Spaying (also called neutering, ovariohysterectomy, or having the uterus and ovaries surgically removed) of female dogs appears to provide a strong protective effect when performed at a young age. Dogs that are spayed before their first heat (estrus), which generally means before the age of 7 to 8 months, have less than a 1% chance of developing mammary gland tumors. The risk increases to approximately 8% after the first heat and 26% after the second heat, which typically occurs around 1 year of age or slightly later. Therefore, it appears that female hormones are a strong influence on the development of these tumors.

If not removed early, approximately 35-50% of mammary gland tumors in dogs are-or become-malignant and spread to other parts of the body (metastasize), most commonly to the lungs and lymph nodes. Once this has occurred, it is very difficult to remove the tumor tissue entirely. Therefore, as in human beings, if a lump is seen or felt in the area of the mammary tissue in a dog or cat, early assessment is essential to reducing the risk of cancerous spread. This is felt as a firm lump on the underside of the chest and belly of female dogs.

Cats develop mammary tumors less often than dogs. Mammary tumor development in cats is also hormone-related. In fact, nearly all mammary gland tumors in cats occur in females that have not been spayed. The majority of mammary tumors in cats are cancerous, and they spread (metastasize) to the lungs and lymph nodes. Cats spayed before 1 year of age have less than a 1% chance of developing these tumors.

Symptoms: Symptoms of mammary tumors include swelling, sores (ulceration), and/or masses on the underside of the chest or belly, namely where the mammary glands are found. If the disease is very advanced, other symptoms such as weakness, decreased appetite, weight loss, and/or breathing difficulty are possible, but these symptoms are vague and may be caused by other illnesses altogether.

Diagnosis: A suspicion usually first arises when either you (the pet's caretaker and companion) or the veterinarian feels a nodule, lump, or growth on the chest or underbelly. However, there are many impostors for mammary tumors, including some processes as simple as the accumulation of normal fat within the breast tissue. Therefore, one or several tests can be used for helping to diagnose mammary gland tumors. Your veterinarian will discuss with you which tests are appropriate for your dog or cat. X-rays of the chest and abdomen can help to determine if metastasis has occurred. An ultrasound examination of the abdomen (belly) can give more specific information regarding the organs that are involved. To definitively diagnose the tumor(s), tissue biopsies of the area are taken under general anesthesia and sent to a laboratory where the tissues are examined by specialists. To assess your pet's overall health, which is required if surgery is performed, routine blood tests such as a complete blood count (CBC) and serum biochemistry profile and a urinalysis are necessary.

Living with the Diagnosis

When a dog or cat is diagnosed with mammary gland tumors, surgery is usually recommended. The intention is to remove as much of the tumor tissue as possible, in the hope that it is removed entirely before it becomes inoperable (as tumors enlarge, they can send tentacle-like projections to surrounding tissues) or spreads to other organs. The outlook (prognosis) depends on many factors including the size and location of tumor(s), whether metastasis has occurred, and the general health of the pet before surgery. The prognosis is better if metastasis has not occurred. Surgery is not helpful for a few types of mammary gland tumors. Your veterinarian will discuss these matters with you before treatment.

After surgery and once your pet is home from the hospital, it is important to give pain medication exactly as directed and to keep your dog or cat as comfortable as possible during the recovery period (usually several days to a week or so).

Treatment

Surgery is performed to remove all of the affected tissue, if possible. The size, number, and location of the tumor(s) generally determine how much tissue or how many glands are removed (mastectomy). Your veterinarian may recommend that an ovariohysterectomy be performed at the time of tumor removal to prevent diseases of the uterus and further hormone release by the ovaries. This is the same surgery as spaying/neutering. An ovariohysterectomy cannot prevent recurrence of mammary gland tumors unless performed at an early age (see above). Chemotherapy, radiation therapy, and hormonal therapy are very rarely recommended after surgery because they are not highly effective. Therefore, the cornerstone of success with mammary tumors in dogs and cats is prevention through spaying/neutering, and early identification and surgical removal if necessary.

After surgery, a bandage may be placed around the patient's chest and/or abdomen to absorb fluids, to gently compress the wound, and to keep it as clean as possible. The bandage should be kept clean and dry at all times and should be snug, but not too tight to make breathing uncomfortable. The bandage typically will be changed as often as needed (at least daily) for the first several days after surgery. A small drain may also be placed in the wound at the end of surgery to help control drainage. This drain is usually removed after several days.

DOs

• Inform your veterinarian if your cat or dog has ever been diagnosed with a medical condition and is taking medication.

• Give medication exactly as directed by your veterinarian, and if you are concerned about possible negative effects, discuss them with your veterinarian immediately rather than simply discontinuing the treatment.

• Do realize the similarities and differences between humans and pets regarding this condition: the importance of early detection and treatment is an important similarity, whereas the extent of mammary tissue (every dog and cat has ten mammary glands) and the very infrequent use of chemotherapy in veterinary patients are important differences.

• Do seek the opinion of a specialist if there is any doubt regarding diagnosis (Is it a mammary tumor or not?) and treatment. Specialists in this field are veterinarians who are also Diplomates of the American College of Veterinary Internal Medicine, Specialty of Oncology.

DON'Ts

• Do not delay contacting your veterinarian if you find a tumor on your dog's or cat's mammary gland.

When to Call Your Veterinarian

• If you cannot keep a scheduled appointment or If you are unable to give medication as directed
• If your dog or cat is not improving after surgery.
• If the surgical site (where the stitches are) becomes increasingly red, swollen, painful, or discharging of fluid.

Signs to Watch For

• As a possible indicator of mammary tumors:

o At any stage: discoloration and/or bleeding on one or more mammary glands, swollen mammary gland(s), discrete tumors that you can feel or see.

o If advanced or during the postoperative recovery period (1 to 2 weeks after surgery): general signs of illness, including lethargy, weakness, decreased appetite, weight loss, and other behavior changes.

Routine Follow-Up

• Patients diagnosed with malignant tumors should be examined by their veterinarian every few months for recurrence of the tumors or metastasis.