Mammary Tumors in Cats are Bad Bad Bad

I'm republishing this article because recently I had two especially sad cases involving mammary tumors in cats.

“Lump on chest” was the brief description in the appointment book for my 4:00 appointment. Todd Pechter had noticed a small, firm lump on his cat, Kina, a 13 year-old spayed female domestic shorthair. He couldn’t be sure how long it had been there; he had only noticed it 4 days ago.

On physical examination, Kina looked fine. She weighed a robust 12 and a half pounds, and appeared to be in excellent health, except for a small, firm mass involving mammary gland #2 on the left side of her chest. The seven other mammary glands felt normal. I informed Mr. Pechter that I believed this to be a mammary tumor and that we should schedule surgery as soon as possible.

It is estimated that one out of 4000 cats develop breast cancer. This may seem like a small incidence, but in fact, breast cancer is the third most common tumor in cats and accounts for 10 to 12 percent of all diagnosed feline tumors.

The average age at onset is 10 to 12 years. Siamese females are at twice the risk of developing this type of cancer compared to other cat breeds. Siamese also tend to develop these tumors at a younger age. Males rarely develop breast cancer. In fact, less than 1% of cats that develop mammary cancer are males.

Intact cats are at an increased risk of breast cancer. Spaying a cat, especially before their first heat, greatly reduces this risk. A hormonal influence is known to exist in dogs, and it is clear that estrogen and progesterone play a similar role in tumor development in cats, although this role is not as well understood. It is hypothesized that, under the influence of hormones, the epithelial cells of the mammary gland enlarge, progressing to a pre-cancerous state, where it continues to grow until it has transformed into a carcinoma.

The benefit of spaying in regard to reducing the risk of mammary cancer in dogs is well documented. Dogs spayed before their first heat have only 0.5% the risk of mammary tumor development compared to an intact dog. After their first heat, the risk jumps to 8%, and after two or three heat cycles, 26%! Spaying a dog after 4 or more heat cycles or after 2.5 years of age has no protective effect. Similar effects are seen in cats. Spaying a cat prior to 6 months of age leads to a 91% reduction in the risk of mammary cancer development. In other words, a cat spayed prior to their first heat (around 6 months of age) has only 9% of the risk of mammary tumor development compared to an unspayed cat. If spayed after 6 months, but before 1 year, the risk is 14% compared to an unspayed female. When Mr. Pechter adopted Kina, she was already somewhere between 2 and 3 years of age, and he did not know for sure at what age she had been spayed.

Typically, a middle-aged or older cat presents to the veterinarian after an owner notices a lump associated with the mammary gland(s). Cats have four pairs of mammary glands: the four on the left side form the left “chain”, and the four on the right comprise the right chain. The glands are numbered one to four, with gland #1 being closest to the head, and gland #4 being closest to the tail. On physical exam, cats may have a single nodule like Kina, or it may have multiple nodules associated with the mammary gland. In dogs, the glands closest to the groin are most often affected. In cats, the tumors occur with nearly equal frequency in all glands, with perhaps a slightly higher incidence in the most cranial (#1) and caudal (#4) glands.

Mammary tumors should be removed surgically. “There is no way to determine whether a mammary tumor is benign or malignant from the visual appearance of the tumor”, says Dr. Avenelle Turner, a board certified veterinary oncologist at the Fifth Avenue Veterinary Specialists in New York City. “The vast majority of mammary masses in cats are malignant, therefore, every mammary-associated lump or mass should be considered malignant until proven otherwise”, says Dr. Turner. Because most of the affected cats are elderly, a full pre-surgical evaluation of the patient is important. A complete blood count, serum biochemistry panel, thyroid evaluation, and urinalysis should be performed. Radiographs should be taken as well, to determine if the cancer has already spread to the lungs at the time of surgery. If the cancer has spread, surgery won’t be curative, and it may be best to cancel the surgery direct all efforts on supportive care to keep the cat comfortable. If the tumor is ulcerated and bleeding or infected, it may be necessary to proceed with surgery even if the tumor has already spread to the lungs or elsewhere. “Changes in the nearby lymph nodes, such as a change in size or texture, may be the first indicator of metastasis”, warns Dr. Turner. “Any enlarged lymph nodes should also be removed at the time of surgery. Some surgeons feel that all nearby lymph nodes should be removed even if they appear normal, because they may contain microscopic disease.”

The goal of surgery is to remove the entire tumor by the simplest procedure possible. Small tumors may be able to be removed via a “lumpectomy”, i.e. removal of just the lump. Larger tumors may need a “mammectomy” – removal of the entire mammary gland. If tumors are present in multiple glands, they maybe removed individually, or via a “chain mastectomy” in which the entire chain of mammary glands is removed, making one long incision. Again, the choice of procedure depends on ease of removal of all affected tissue. Because each gland within a mammary chain is connected to each other by lymphatic vessels, some surgeons feel that a radical chain mastectomy is the procedure of choice, since mammary tumors initially spread via the lymphatic vessels. Kina’s tumor, at 2 centimeters in diameter, required a mammectomy.

In dogs, 50% of these tumors are benign. Of the 50% that are malignant, half of them can be removed completely, resulting in a cure. The other half will either recur or metastasize (spread to other parts of the body) following surgery. In cats, the picture is more grim: approximately 86% are malignant. Not surprisingly, Kina’s mammary tumor fell into this category; it was a malignant mammary carcinoma, however, no invasion of the lymphatic vessels by cancer cells was seen by the pathologist, and he reported that the mass appeared to be completely removed.

There are differing opinions regarding the efficacy of chemotherapy for feline mammary gland tumors. Chemotherapy is often recommended as adjunct therapy in cats whose tumors show evidence of invasion into the blood vessels or lymphatic vessels. Others recommend chemotherapy in all cases, given the high metastatic potential of feline mammary tumors. A consultation with a veterinary oncologist would be prudent to assess whether a particular cat is an appropriate candidate for post-surgical chemotherapy.

Prognosis depends on several factors, the most important being the size of the tumor at the time of diagnosis. If the tumor is less than 2 centimeters in diameter, the prognosis is better; cats often survive over 3 years. Tumors larger than 3 centimeters are associated with a survival time of only 4 to 6 months. These statistics clearly illustrate what has essentially become common knowledge regarding cancer in people and animals: early detection is of paramount importance. This fact cannot be overstated. Kina’s tumor, at 2 centimeters, was relatively small, and her pathology report looked favorable, however, almost exactly a year after her tumor was removed, she presented to our office with difficulty breathing, and x-rays revealed several small masses in the lungs as well as some fluid in the chest cavity. Analysis of the fluid confirmed the presence of carcinoma cells. Pulmonary metastasis (spread of the cancer to the lungs) is the most common cause of mammary-cancer related death, and sadly, Kina succumbed to her illness soon afterward.

I examined Catalina, a cat that was owned by one of my very first Manhattan Cat Specialists clients. The owner had found Catalina at a building site, pregnant. He adopted her, and she was spayed after she had the kittens. Three months prior, he brought Catalina in for an exam because of two lumps on her abdomen. On physical exam, I could see that these were mammary tumors, and one of them was pretty angry looking. The fact that more than one gland was involved was an ominous sign, suggesting that cancer cells had most likely invaded the lymphatic channels that connect the glands. This increased the risk that tumor cells were in other places of the body, as well. I took chest x-rays, and they were clear. The resolution of an x-ray is limited, however, and masses smaller than 2 mm will not show up on an x-ray. With the chest being clear, we went ahead and did a radical mastectomy, removing all of the glands on the left side.

The histopathology report revealed an aggressive mammary adenocarcinoma.

Catalina presented for coughing and breathing hard. I could see in the exam room that indeed, she was exerting more effort breathing than she should be for a cat at rest. I told the owner that I needed to take chest x-rays again. He consented, and the x-rays revealed the lungs to be full of multiple nodules. This was metastatic mammary adenocarcinoma. At this stage, there were no treatment options. We put Catalina to sleep, which was truly heartbreaking.

The next day, I noticed on my busy Saturday appointment book that "Big Mama" was coming in for an exam. In the appointment book, it said "weight loss and breathing hard". Oh no. I had removed an aggressive mammary carcinoma from her a few months ago. When the tumor was first noticed, it wasn't terribly big. I urged the client to schedule the appointment as soon as possible, but they somehow kept delaying the procedure. I finally managed to get them into our hospital for surgery about 2 months after the tumor was first noticed. Although Big Mama's chest was clear at the time of surgery, and the surgical margins around the tumor were free of any cancer cells, mammary tumors in cats are aggressive, and I warned the clients about the possibility of the tumor spreading.

I examined Big Mama, and the first thing I noticed was that Big Mama wasn't big anymore. She had lost almost 3 pounds. The owners thought it might be because they admittedly weren't being very consistent about giving Big Mama her thyroid medication. They thought her coughing and breathing hard might be due to asthma or maybe a cold. Unlike Catalina's owner who was expecting the worst, Big Mama's owner clearly was not expecting what I knew I was going to have to tell her.

I took x-rays of the cat, hoping for something not too bad, but sadly, the films were exactly like the ones I had taken of Catilina's: a chest full of nodular masses. I had to break this terrible news to the owner, who of course was shocked. Fortunately, Big Mama was still eating and wasn't in any discomfort, and we did not put her to sleep, but I fully expect to see her back in my office in, at most, a few weeks, to be put to sleep.

If you're reading this now, and you have a cat who was spayed later in life, check your cat's belly right now, for any lumps or bumps. Do this every week. Forever. For mammary tumors in cats, early detection is absolutely key to survival. If anything feels weird, notify your veterinarian immediately.


  1. Thank you so much for posting/re-posting this article. We just lost another lovely cat in less than a year, to aggressive mammary adenocarcinoma. Our case was a bit different in that both of our cats were about 6-7 years old, the first had been spayed at about 3 years old, she was a rescue, and the second was spayed at less than 2 years old.

    As a former vet tech, I understood the need to spay, and watch them, but I also knew that most commonly this type of cancer struck older cats...I wish I had been more on top of things, as Artemis the one we just helped pass, went through more than I would have liked with bleeding from both her ears and nose 3 weeks after her radical chain mastectomy.

    Our vet still doesn't know (without a necropsy) what caused the bleeding, and we couldn't bear the thought of having one done.

    We are still very concerned, due to the fact the two younger cats had no genetic relation, were indoor only, in a closed household, struck by the same type of cancer, that there is an environmental carcinogen in our home. It seems too strange to believe it is simple coincidence.

  2. my cat has multiple lumps. She is ten months old and just went into heat a month ago, she has never been around a male. 2 weeks ago she had one lump--now its bigger and has lots of company;at least 6]
    I am on ss and dont have much money--help!!I love Snowy!!! Any ideas?

    1. Should of removed the tumors when they were small.

    2. Get her spayed and see if lumps go away as hormones could be causing condition, or while she is getting spayed ask if they can remove lumps and get biopsy.

  3. I have a 12 year old female cat I rescued at 3 weeks old about to be thrown into a garbage truck. we became mother and daughter so to speak- I traveled with her and spoiled her to death. Just a few months ago I noticed a grape sized lump under her right arm, came out of no where?? so I ran my hand across her stomach and found about 5 or 6 pea size knots as well. After an immediate visit to the vet an probability of Mammery cancer, I decided to let Sarafina live out her life. She not showing discomfort yet but the 3rd nipple down is about to explode. I also noticed she is sleeping much more. She is an Alpha Alpha female with other cats but a tender hearted social butterfly around people. Should I put her to sleep now or wait.

    1. The article says to have lumps removed when small.

  4. I found my female orange tabby, Pumpkin, wandering outside back in 2003. I took her in, and my vet estimated her to be between 3-5 years old. She was not spayed, but I immediately scheduled her for a spay.

    In 2008, I noticed a lump on one of her mammary glands, and I brought her to my vet, who scheduled her for a lumpectomy.

    A short time after the surgery, I noticed that the lump had returned as well as a few additional pea sized lumps in both chains. I returned to my regular vet, who referred me to a surgeon for a bilateral masectomy of both mammary chains.

    I scheduled the surgery in August of 2008. Her recovery afterward was difficult. She had to stay overnight because she was having difficulty breathing, due to her skin being pulled tightly. I worried that I had mad the wrong choice, but she eventually recovered.

    When the histopath report came back, the surgeon called me and reported that it was cancer. I made the decision that I would not put her through any additional surgery to remove any lumps. If the cancer came back, I decided that I would allow her to live until her quality of life deteriorated, and then I would have her euthanized.

    It is now September 2011, and it has been over 3 years since Pumpkin's surgery. She is alive and well with no signs of cancer. She is truly a survivor.


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