By DR. KARSTEN FOSTVEDT
Breast tumors, or mammary gland tumors, are benign or malignant masses that develop in breast tissue. They usually affect older female dogs. They are the most common tumors found in female dogs. These tumors usually occur in unspayed females, or in dogs that were spayed later in life.
The risk of developing mammary tumors is directly related to the number of heat cycles the dog has experienced. If the dog is spayed before the first heat cycle, the risk is 0.05 percent. Relative risk increases to 8 percent after one heat cycle and to 26 percent after a second heat cycle.
Any swelling in the mammary glands should be brought to the attention of your veterinarian. The mammary gland closest to the rear legs is most commonly affected. Mammary masses that are reddened and painful and ulcerated are usually malignant. Many malignant breast tumors will spread to other organs (metastasis).
When a lump in the mammary gland is noticed, aspiration of the mass with a fine needle often helps determine whether the tumor is benign or malignant. Similar aspirations of nearby lymph nodes may help to detect metastasis. Chest X-rays and blood tests are also important before any tumor surgery is performed.
If the fine needle aspirate is benign (which is 60 percent of the time), then no surgery is necessary. If the fine needle aspirate shows malignant or cancerous cells, then surgery is necessary to remove the tumors. A number of surgical procedures are available for treating these tumors. They range from a simple lumpectomy to a radical mastectomy, removing all five mammary glands on one side of the dog (there are five mammary glands on each side of the dog’s abdomen).
Radiation and chemotherapy have not been effective for treatment of mammary tumors in dogs.
Most dogs do well following surgery for mammary tumors. Many require hospitalization. Many with simple lumpectomies are “day procedures” and go home that day. Periodic laboratory tests and X-rays may be done to monitor for metastasis if the tumor was malignant.
Prognosis for benign tumors is good, especially if surgical removal is performed. Dogs with malignant tumors less than 1.5 inches in diameter have a better prognosis following surgery than those with larger tumors. The presence of multiple tumors does not seem to affect the prognosis. Survival for longer than two years is possible for low-grade cancers. Tumors that have metastasized have a very poor prognosis. Please spay your dog early to prevent these tumors; and if you feel a mammary gland mass, have your veterinarian evaluate it immediately.
Dr. Karsten Fostvedt is a veterinarian at St. Francis Pet Clinic in Ketchum.
