Cancer affects roughly 30% of cats over age 10, making it the leading cause of death in older felines. The challenge is that cats are masters at hiding illness, so the signs often look subtle or mimic other conditions. Knowing what to watch for can help you catch a problem early, when treatment options are broadest.
Lumps That Need Attention
Not every lump is cancer, but no one can tell the difference just by looking or feeling. Even experienced veterinary oncologists cannot determine whether a mass is malignant by touch alone. Cancer is a cellular diagnosis, meaning it requires lab work to confirm.
The general guideline veterinarians use: if a lump reaches the size of a pea (about 1 cm) and has been present for a month, it should be tested. You should also have any mass evaluated if it’s growing, changing in appearance, or seems to bother your cat. Visual monitoring alone isn’t enough. If you find a lump, note its size so you can track whether it changes over time.
Mammary tumors deserve special urgency. In cats, roughly 90 to 93% of mammary tumors turn out to be malignant. That’s dramatically higher than in dogs. If you feel a firm lump near your cat’s nipples or along the belly, get it checked promptly.
Skin Changes That Come and Go
Squamous cell carcinoma, one of the most common feline cancers, often starts as something that looks completely harmless: a tiny scab, a small scratch, or a flaky patch. It may even disappear for a while and the skin will look normal. But it comes back, sometimes months or even a year later, and gradually worsens.
As the tumor progresses, you’ll notice swelling around the lesion and tissue erosion. The sore may ooze fluid, develop irregular hardened borders, and cause hair loss in the surrounding area. The most common locations are the temples, the outer tips of the ears, eyelids, lips, and nose. White or light-colored cats are at higher risk because these areas have less pigment to protect against UV damage.
The key red flag is a sore that won’t fully heal. A normal scratch or scrape resolves within a couple of weeks. A wound that keeps coming back in the same spot warrants a vet visit.
Mouth and Eating Problems
Oral squamous cell carcinoma is particularly common in cats and easy to miss early on. The first thing most owners notice is that their cat stops eating or loses weight. But the cat isn’t refusing food because they’ve lost their appetite. They’re hungry and may approach the food bowl, sniff at it, and walk away because eating is painful.
Other signs to watch for:
- Blood-tinged saliva around the mouth, in the water bowl, or on the front paws
- Foul breath that’s noticeably worse than normal
- Excessive drooling
- Swelling along the jaw or chin, or visible facial deformity
- Decreased grooming, leading to a matted or unkempt coat
- Loose teeth as the tumor invades the jawbone
Inside the mouth, these tumors often appear as ulcerated open sores along the gum line that distort the underlying bone. You likely won’t see this yourself unless you’re in the habit of checking your cat’s mouth, which is one reason routine veterinary exams matter.
Unexplained Weight Loss
Unintended weight loss is one of the most reliable warning signs across many types of feline cancer. Cancer cells hijack your cat’s metabolism. They can decrease nutrient absorption and increase the body’s energy demands, causing weight loss even when a cat is still eating well.
This is especially true with gastrointestinal lymphoma, the most common form of lymphoma in cats. The signs overlap heavily with everyday digestive issues: decreased appetite, soft stools or diarrhea, vomiting, and gradual weight loss. Any one of these symptoms alone might not raise alarms, but when they persist for weeks or appear in combination, they point to something more serious than a sensitive stomach.
Litter Box and Bathroom Changes
A litter box that stays too clean is always a concern. If your cat is producing less urine or stool than usual, tumors may be blocking the urinary or gastrointestinal tract. Straining to urinate or defecate, blood in the urine or stool, or going outside the box can all signal a problem. These symptoms have many possible causes, but cancer is one of them, particularly in older cats.
What the Vet Will Do
If your vet suspects cancer, the diagnostic process typically starts simple and gets more detailed as needed.
A fine needle aspirate is often the first step. The vet inserts a thin needle into the mass, withdraws a small sample of cells, and examines them under a microscope. It’s quick, inexpensive, and can be done on any lump your vet can reach. For certain tumor types, this alone provides a definitive answer. For others, it narrows the possibilities but isn’t conclusive enough to plan treatment.
When more information is needed, a biopsy provides a larger tissue sample. This can mean removing the entire mass (if it’s small, under about 3 cm, freely movable, and not attached to surrounding tissue) or taking just a piece. The tissue goes to a pathology lab, where it’s examined in detail. Deep biopsies, going more than a centimeter into tissue, are sometimes necessary to avoid sampling only the surface layers and missing the tumor underneath.
Ultrasound is commonly used to look at what’s happening internally. It can reveal whether a tumor is near major blood vessels, whether cancer has spread to lymph nodes or organs, and whether a suspicious mass is solid or fluid-filled. Depending on the situation, your vet may also recommend blood work, X-rays, or other imaging.
Why Early Detection Is Difficult
Cats instinctively mask pain and illness. A cat with an internal tumor may act perfectly normal until the disease is advanced. Weight loss often happens so gradually that you don’t notice until your cat has lost a significant amount. Behavioral changes like decreased activity or sleeping more can easily be chalked up to aging.
The most practical thing you can do is get in the habit of running your hands over your cat’s body regularly, feeling for lumps or areas of tenderness. Weigh your cat monthly if possible, since catching a downward trend early is much easier with actual numbers than with visual impression alone. And pay attention to small, persistent changes: the sore that keeps reappearing, the food bowl that’s slightly less empty, the grooming that’s slightly less thorough. In cats, subtle and persistent is the pattern that should prompt a vet visit.