Case of the Month Archives - Summer 2006

Sophie Mink - Mammary Tumor in a Dog

Sophie Mink is a 12 year old female, spayed labrador retriever who presented to our hospital 3 months ago for evaluation of a tumor in her mammary region. The tumor had been recently found by her owner. In addition to the tumor, Sophie’s owner has also noticed other changes in her health. Her owner was concerned about some weakness and stiffness that Sophie was exhibiting in her hind legs. Sophie’s owner was also concerned about her harsh and heavy breathing. One important piece of information regarding her medical history was that Sophie was spayed as an adult dog. Sophie was bred and did have a litter of puppies.

Sophie’s physical exam revealed a large mammary tumor on her right side. Sophie was also found to be 10 lbs. overweight and having arthritis in her knees. Her breathing was indeed found to be very harsh and there was some concern as to whether the larynx was properly opening to allow air into her airway. After her extensive physical examination, surgical removal of the tumor was recommended.  In preparation for her surgery, a complete blood count, a urinalysis, a thyroid level and a chemistry panel was performed on Sophie.

Sophie’s bloodwork showed some elevated liver enzymes, elevated cholesterol and triglyceride levels and a low thyroid level. Her CBC (complete blood count) and urinalysis were normal.

Sophie was placed on thyroid hormone supplementation for several weeks. Her thyroid level was rechecked and found to be at a normal level. Her harsh breathing was also improved on the thyroid hormone supplementation. Once her thyroid level was normalized, we scheduled her surgery for the mammary tumor removal .

Prior to her surgery, chest radiographs (x-rays) were taken to ensure that there was no evidence of metastasis (spread of the tumor). Her chest radiographs were normal and surgery was performed.  A large mammary tumor, the size of a baseball, was removed and submitted to a laboratory for analysis. The tumor was diagnosed as a mammary adenocarcinoma. The surgical margins were clean and wide which means that there were no tumor cells left behind in her body.

Tumors of the mammary gland are the most common tumors of female dogs. Mammary tumors account  for approximately half of all cancers in the unspayed female dog. Mammary tumors have been reported to occur in approximately 2 of 1000 female dogs. Approximately half of the canine mammary tumors are malignant or cancerous i.e. adenocarcinoma. The remaining tumors are benign i.e. adenoma. Surgical removal of a mammary tumor is the treatment of choice for benign mammary tumors and for malignant mammary tumors that  have not spread beyond the mammary tissue and nearby lymph nodes. Most benign tumors are curable by surgery. Approximately half of the malignant mammary tumors are cured by surgery. This is possible because some malignant tumors in the dog do not spread very quickly and can be removed before they spread. “Radical” mastectomy has not been shown to be any more effective than more limited surgery. Tumors that are larger than 3 cm and that are of a higher grade (as classified by the pathologist) are more likely to recur with 70% recurrence at 1 year. Smaller tumors and tumors of a lower grade can have 30% recurrence at a year. An effective chemotherapy protocol for canine mammary cancer has not been defined. A small percentage of dogs have had partial remission with drugs such as doxorubicin or cisplatin. Because surgery alone is successful in many cases and chemotherapy has not been successful in many cases, chemotherapy has been reserved for tumors that cannot be surgically removed with clean margins. Radiation has not been studied to any extent in dogs with mammary tumors. It is important to note that mammary cancer can be prevented in the dog by early ovariohysterectomy (spaying). The risk of developing mammary tumors in dogs has been reported to be 0.05% for dogs spayed before their first heat cycle (estrus), 8% for  dogs spayed after their first heat cycle and before the second heat cycle, and 26% for dogs spayed after the second estrus. Therefore, dogs that are not going to be used for breeding purposes should undergo early ovariohysterectomy.

Sophie’s case is important for several reasons:

1. Performing appropriate bloodwork and urinalysis testing PRIOR to surgery is very important. For any age patient, preanesthetic blood testing can detect underlying organ abnormalities that may pose an increased risk for anesthesia. In Sophie’s case, her thyroid level was low. Hypothyroidism is a commonly diagnosed disorder in older dogs, especially labrador retrievers. Patients with low thyroid levels may not tolerate certain narcotic medications or metabolize them normally. This could cause a slower recovery time from anesthesia for these patients. Preanesthetic bloodwork can provide crucial information that can help stabilize a patient prior to an anesthetic or surgical procedure.
   
   
2. Chest radiographs (x-rays) are important to perform prior to mammary tumor removal surgery. If a patient has suspicious nodules in their chest, this likely means that the cancer has already spread. This may change the decision of the owner to pursue surgery.
   
   
3. Intact females have a seventeen fold increased risk of developing mammary cancer compared to neutered females. Spaying prior to the first estrus cycle significantly reduces the risk of mammary tumor development in dogs.

Currently, Sophie is doing very well at home. She is still receiving daily thyroid hormone supplementation. She is breathing more easily and her weakness is slowly improving. She also appears to have more energy than she did before her surgery. Sophie has lost 5 lbs. since her surgery and has made a complete recovery. We will continue to monitor Sophie closely  with regular follow-up visits. We will monitor her mammary region for recurrence of tumors or development of tumors in other areas along her mammary chain.