October 2026
You're giving your rat a cuddle and your fingers find it: a lump under the skin that wasn't there last week. It's an unsettling moment, and a very common one. Mammary tumors are among the most frequent health problems in pet rats, especially females, and lump removal is one of the surgeries I perform most often. The reassuring part is that most of these tumors are benign, and surgery usually goes well when the lump is removed early.
Mammary tumors are growths that start in the mammary (breast) tissue. Rats have mammary tissue across a surprisingly large area of the body, from the neck and shoulders down to the belly and groin. That's why a mammary tumor can show up in places you might not expect, such as the armpit, the side of the chest or near the base of the tail.
Most mammary tumors in rats are benign, meaning they don't spread to other organs. Even so, they can grow quickly and become very large. A big tumor can make it hard for your rat to walk, groom or eat, and the skin over it can break open. Male rats can get mammary tumors too, though it's much less common.
The main sign is a soft or firm lump under the skin, often one that moves when you touch it and grows over time. As a lump enlarges, you may notice difficulty walking, climbing or grooming, a scab or sore on the lump, less activity, hiding or a smaller appetite. Red-brown staining around the eyes or nose often shows up when a rat is unwell and grooming less.
Make a habit of gently running your hands over your rats' whole bodies during handling time. Finding a lump while it's small makes surgery simpler and recovery faster.
Surgical removal is the most common and effective treatment. Your rat is placed under general anesthesia and the lump is carefully removed. Many rats are back to normal activity within a few days. Removed tumors are often sent to a lab to confirm the type.
Because rats have so much mammary tissue, new tumors can develop later, even after a successful surgery. We may discuss spaying at the time of lump removal, or medication that may help reduce the chance of new tumors. I'll talk through these options with you based on your rat's age and health.
Older rats commonly have kidney changes that don't show from the outside. Before anesthesia, and before any long-term anti-inflammatory medication, bloodwork and sometimes a urine test help me choose the safest plan.
The best way to lower the risk of mammary tumors in female rats is spaying. Spaying a young female before she matures greatly reduces her chance of developing mammary tumors later in life, and it also prevents uterine disease and surprise litters. Ask about the best timing for your rat.
Keep your rat in a clean, simple cage for a few days, with paper towels or fleece instead of loose bedding. Some pain medications can make rats chew and eat non-food material, so I often suggest removing anything they might swallow during recovery. Take down tall shelves and hammocks for a while so they don't strain the incision, and offer favorite foods to encourage eating. Give pain medication exactly as prescribed, even if your rat seems fine, and check the incision daily. Stop cage mates from grooming or chewing at it.
Rats often hide pain when someone is watching. Signs your rat is uncomfortable can include a poorly built nest, less exploring or rearing up, less grooming, or an unusual posture. A short video taken when your rat doesn't know you're there can be surprisingly useful.
Call the same day if your rat is not eating, seems lethargic, is breathing hard or noisily, or has a problem with the incision after surgery.
Book a prompt visit for any new lump, a lump that is growing quickly, has opened or is bleeding, or a rat who is struggling to move, eat or groom.
As Nashville's exotic companion mammal specialist, Dr. Logan Kopp offers lump removal, spaying and follow-up care for pet rats at Priest Lake Veterinary Hospital. Call (615) 361-4646 to schedule a visit.
This article is general information, not medical advice for your pet. Reading it doesn't create a veterinarian-client-patient relationship (VCPR). Please talk with your own veterinarian before making changes to your pet's care.