What Are Mammary Tumors?
A mammary tumor is a tumor of the mammary gland. Cats have four pairs of mammary glands along their underside, starting with glands near the axillary (armpit) region and extending backward to the glands in the inguinal (groin) area. A set of four glands along the body’s left or right side is called a mammary chain.
85% of feline mammary tumors are malignant, meaning they have the potential to spread throughout the body. These are the most concerning tumors cats develop. There are several different kinds of malignant mammary tumors. Cats often develop more than one malignant tumor type in different glands. Benign tumors, which are tumors that do not have the potential to spread, are uncommon.
Un-spayed cats have a seven-fold higher risk of developing mammary cancer than spayed cats. Male cats can also develop mammary tumors.
What Are The Clinical Signs?
Many cats show no signs related to a mammary tumor. You might feel a lump while petting your cat, or a groomer may notice a mass. Your veterinarian may also discover a mass during an exam.
Some tumors can be ulcerated or bleed. Cats may lick the affected gland(s). If cancer spreads (metastasizes), cats can show weight loss, poor appetite, vomiting, diarrhea, or breathing difficulties.
The best chance for long-term control is if the tumor can be diagnosed early when it is smaller than 2cm. Contact your veterinarian if you notice any lumps or bumps along your cat’s belly or chest region.
What Diagnostics Are Performed?
A complete physical exam will look for signs of disease. If a mass is noted, your veterinarian may use a small needle to take a sample from the growth. This is called a fine needle aspirate. This test can rule out other tumors that can look like a mammary mass. A diagnosis of a mammary tumor is confirmed with a
biopsy, which is also the most reliable way to distinguish between benign and malignant masses.
A complete blood count, serum chemistry panel, and urinalysis are performed to determine whether the cancer affects body functions and ensure your cat is healthy enough to handle future treatments.
Mammary tumors can spread to lymph nodes. These are often in the axillary and inguinal regions but may also be inside your cat’s body. A small needle is used to take cell samples from these lymph nodes to check for spread. Chest X-rays and abdominal ultrasound look for spread to the lungs and internal organs
or lymph nodes. In some cases, a CT scan or MRI is recommended. Results determine your pet’s treatment options and prognosis.
What Are The Treatment Options?
Surgery
Wide surgical resection is recommended for malignant mammary masses. Because mammary tumors are more likely to be aggressive in cats, and they tend to develop more than one tumor, we recommend removing all four glands on the same side as the tumor rather than just the lump. This is called a radical full-chain mastectomy.
The most aggressive plan is to remove all the mammary tissue on both sides, even if there is only one tumor present on one side. This is called a bilateral radical mastectomy. Surgery is done on one side, followed by a recovery period of 2-3 weeks, then surgery is done on the other side. Pain medications are essential after surgery.
We still recommend removing benign tumors, but the surgery can be less aggressive.
Radiation Therapy
Radiation therapy has not been studied for treating mammary tumors in cats despite playing a significant role in treating this disease in people. Radiation can be done before or after surgery or in cases where the tumor is inoperable.
Chemotherapy
Chemotherapy is usually recommended for cats with malignant mammary tumors. Protocols vary but typically involve injectable doxorubicin or mitoxantrone either alone or in combination with one or more drugs (carboplatin, cyclophosphamide, others.) The goal of this form of chemotherapy is to kill any microscopic cancer cells present after surgery. Chemotherapy can be used to treat tumors that cannot be removed with surgery or for cats where surgery is not an option due to other health concerns.
An alternative to these injections is metronomic chemotherapy, which entails low-dose oral chemotherapy given at home. This treatment plan aims to starve the tumor cells of their blood supply and stimulate the cat’s immune system to fight the cancer cells.
Non-steroidal anti-inflammatory Drugs (NSAIDs)
NSAIDs play a role in treating many different types of tumors. Some cats with mammary carcinoma benefit from receiving an NSAID. Bloodwork to monitor kidney function is required.
Examples of chemotherapy drugs used to treat cat mammary tumors are shown in the table below.
| Drug | How Is It Given? | How Often Is It Given? | Approximate Cost* |
|---|---|---|---|
| Doxorubicin (+/- carboplatin) | Intravenously | Every 3 weeks for 6 treatments total | $400-600 per treatment |
| Metronomic chemotherapy (e.g., low dose cyclophosphamide + NSAID, Palladia, etc.) | Orally (at home) | Daily | $600 per month |
| NSAID alone | Orally (at home) | Daily or less frequent | Varies - does require periodic blood work |
What Is The Prognosis?
The prognosis for cats with mammary tumors is variable. Cats with one small tumor (< 2 cm) can survive several years after aggressive surgery. Cats with larger tumors (> 3cm), metastases, and certain subtypes (determined by biopsy after removal) only have a life expectancy of a few months. To ensure the most optimal outcome, we recommend adding chemotherapy after surgery for nearly all cats with mammary tumors. However, the benefit of adding chemotherapy after surgery is inconsistently proven in studies.
How Do I Prepare?
We understand this is a difficult time and support you and your pet. Some owners find it helpful to come to their appointments with a list of questions. Your primary veterinarian can also help you determine
what questions to ask.
We will update you on your cat’s status at each appointment and discuss recommendations based on your pet’s response. Treatment plans can change or stop at any point.
Getting Started
Once you have determined the best option, we will work with you to develop an appointment plan. Appointments for patients undergoing treatments and rechecks must be scheduled in advance. All recheck appointments are drop-off appointments.
Drop-offs are between 7:30 am-8:30 am.
Pick-ups occur by 6:00 pm.
No discharges occur between 2:30-3:30 pm as our oncology team is in rounds.
*Costs are estimates. The overall cost depends on patient response. Estimates do not include supportive care or hospitalization.
