"Hi, Mrs. Knode. How are you doing today?" I asked the client coming into the exam room.

"I am doing fine, Doc, but Muffin here has a problem. I think she has a lump on one of her teats."

I had Mrs. Knode put Muffin, a nine-year-old poodle, on the exam table. "When did you first notice the lump?" I asked as I examined Muffin's mammary glands. I felt a nodule about an inch in diameter in one of Muffin's last mammary glands.

"I just noticed it the other day," said Mrs. Knode.

The nodule was firm and distinctive from the rest of the tissue in the mammary gland. I checked the other mammary glands again. I did not feel any other lumps. I finished checking Muffin, feeling her lymph nodes. None of them was enlarged. The rest of her exam was fine.

"We need to remove this lump," I said to Mrs. Knode. "We can then send it off for a biopsy to see if it is malignant or not."

"Can't you tell if it is malignant by the way it looks?" asked Mrs. Knode.

"Unfortunately not," I answered. "Certain things can make us think that a tumor is malignant, like open sores right where the tumor is or enlargement of the lymph nodes, but the lack of these things does not eliminate the possibility of the tumor being cancerous. The only way to tell for certain is to do a biopsy. We should also spay Muffin at the time of surgery. Unspayed dogs are seven times more likely to develop mammary tumors than spayed dogs. Estrogen production appears to have some relation to the development of these type of tumors.

"How has Muffin been doing otherwise? Is she eating okay? Any vomiting or diarrhea? Any coughing?"

"She has been doing fine otherwise, just her typical worrisome little self. She has a good appetite. I have not seen any vomiting or diarrhea, and I have not noticed any coughing."

"Good," I said. "We will do some pre-surgical bloodwork on Muffin just to check her little system out. We want to make sure that her organs, like her liver and kidneys, are functioning properly before putting her under anesthesia."

We took Muffin back to the lab and drew the bloodwork. She was nervous but she did really well for us. She did not put up much of a fuss, and we were able to get the blood easily. I took Muffin back to her mom.

"I will have the results of this bloodwork tomorrow," I told her. "I'll give you a call when it comes in."

The bloodwork came back the next day. It was fine. I called Mrs. Knode and told her the results. She was pleased that there were no other problems. We went ahead and set up the appointment for the surgery.

A few days later, we did surgery on Muffin. It went smoothly. We sent the mammary tumor off to have a biopsy done on it. The biopsies usually take about a week to come back, so we sent Muffin home while we waited for the results.

The mammary tumor is the most common tumor in the dog. Two out of every one thousand dogs are at risk, and fifty percent of these are malignant. Although there is no clear tendency for one breed to develop this over another, some studies have suggested a higher incidence in spaniels, poodles, and terriers.

Owners can do things for their pets to decrease the chances of cancerous mammary tumors developing. Spaying done prior to the dog's first heat cycle has been found to be protective against the development of malignant mammary tumors. Spaying done between the first and fourth heat cycles offers protection as well, although not as much as doing it before the first heat.

High fat diets have been associated with the development of malignant mammary tumors in humans and possibly in dogs. Studies have shown that dogs that are thin at nine to twelve months of age are at a reduced risk compared to other spayed dogs. So feeding your dog a good dog food, not over-feeding it, and not feeding it table scraps could help to prevent your dog from getting a malignant mammary tumor.

We got Muffin's biopsy back a few days after the surgery. Thankfully, it came back benign, meaning it was not cancerous. Both Mrs. Knode and I were ecstatic. If Muffin's biopsy had come back malignant, we would have had to do x-rays on Muffin's chest to look for evidence of the tumor there. The lungs are one of the first places to which cancerous mammary tumors tend to spread. We would also have had to discuss the option of chemotherapy to try to prevent spreading of the tumor.

Thankfully, we did not need to pursue further treatment for Muffin's tumor. Other dogs might not be so lucky. Do what you can to prevent your dog from developing a malignant mammary tumor. Get her spayed as soon as possible, preferably before the first heat. Some veterinarians consider February as being the spay/neuter month and may be doing some kind of promotion. If you have not gotten your pet spayed or neutered, check with your veterinarian about doing it this month. We want all of our pet owners to have happy endings like Muffin.

-Dr. Reggie Cox practices at Prime Care Animal Hospital, Inc. a small animal practice in Gambrills, Maryland. Dr. Cox is a graduate of the University of Missouri, Columbia.