Oral Tumours: Canine Melanoma and Feline Oral Squamous Cell Carcinoma

The trouble with the mouth is that it does its job out of sight. A small mass on the gum, under the tongue or right at the back of the throat can grow for weeks before it interferes with anything you'd notice. The early signs are vague and easy to put down to something ordinary: bad breath blamed on dental disease, a bit of drooling, eating more slowly, dropping food, pawing at the face, or a reluctance to have the head touched. Blood-tinged saliva or a swelling of the face or jaw usually comes later (NC State Veterinary Hospital, 2024).

Cats are especially good at hiding it. A cat with a sore mouth often just goes quiet, grooms less, hides more and eats a little less, and those signs are so subtle and so unspecific that owners genuinely have no way of knowing what's behind them until the tumour is large (NC State Veterinary Hospital, 2024). None of this is a failing on your part. It's the nature of the place these cancers grow. The one thing that helps is the simplest thing there is: lifting the lip now and then for a look, and getting any mouth change, smell or eating difficulty checked rather than waited on. Our piece on the warning signs of cancer goes through what's worth watching for.

Melanoma is the most common mouth tumour in dogs (Dr Buzby's ToeGrips, 2024). It usually shows up as a dark or sometimes pink mass on the gum, lip or palate, often with drooling, a smell, bleeding, loose teeth or trouble eating (Dr Buzby's ToeGrips, 2024). It behaves badly in two ways at once. Locally it invades the surrounding tissue and often the jawbone, and it also tends to spread, commonly to the local lymph nodes and then the lungs. In one study of dogs with oral melanoma, around 40% of those whose mandibular lymph nodes felt a normal size turned out to have cancer in them anyway (Williams & Packer, 2003). That's why your vet will want to check the nodes and the chest, not just the mouth.

Treatment usually starts with getting local control: surgery to remove the mass with a wide margin, which for a jaw tumour can mean removing part of the jaw, and dogs generally cope far better with that than owners expect. Radiation is the other main local treatment, particularly when surgery can't get clear margins or the site won't allow it, and melanoma tends to respond well to it (BluePearl, 2024). There's also the canine melanoma vaccine (sold as Oncept), a treatment that primes the dog's own immune system against the tumour and is given after the visible disease has been controlled. I'll come back to how much it actually delivers in a moment.

The outlook depends enormously on size and position. Small tumours near the front of the mouth do considerably better than large ones at the back (Dr Buzby's ToeGrips, 2024). With surgery to gain local control, reported median survival sits broadly in the range of several months to over a year, with radiation in a similar bracket; left untreated, melanoma progresses fast, with a median survival of only a couple of months (Dr Buzby's ToeGrips, 2024). "Median" means the midpoint, so half of dogs live longer, and our guide to reading a prognosis explains why a range is the truthful answer rather than a date.

A word on the vaccine, because it's where hope and evidence pull against each other. The licensing study suggested dogs given it after local control lived longer than historical comparison dogs, and it's very safe (Pellin, 2022). But several later studies that compared vaccinated and unvaccinated dogs more directly found no clear survival difference (Ottnod et al., 2013; Verganti et al., 2017; Pellin, 2022). So it's a reasonable, low-risk addition that some oncologists offer, not a proven cure-all, and it's worth asking your vet to lay out the real expected benefit before you decide. Our piece on real hope versus hype is built for exactly these conversations.

I won't soften this, because you deserve the truth and then the kindness. Oral squamous cell carcinoma is the commonest mouth cancer in cats, making up around 70 to 80% of feline oral tumours (Today's Veterinary Practice, 2016). It typically grows on the gum, under the tongue or at the back of the mouth, invades deeply and quickly, and because cats hide their discomfort, most are found when the tumour is already large and can't be fully removed (NC State Veterinary Hospital, 2024).

The hard part is that no treatment has reliably worked against it. Surgery, radiation and chemotherapy have all been tried, and across them median survival is usually only around two to four months, with fewer than one in ten cats alive a year after diagnosis (NC State Veterinary Hospital, 2024). Cats with a small tumour right at the front of the lower jaw that can genuinely be removed do better, but they're the minority (NC State Veterinary Hospital, 2024).

What this means in practice is that for most cats the kindest, most realistic goal is comfort rather than cure. A cat with this tumour that won't eat is in pain, not simply off its food, and keeping that pain controlled is the heart of good care here (NC State Veterinary Hospital, 2024). That can include strong pain relief, anti-inflammatories, sometimes a short course of palliative radiation that eases discomfort for a while, and help with eating. Our piece on managing pain and comfort goes into how that's done well. Choosing comfort-focused care for a cat with oral SCC isn't giving up on them. It's often the most loving thing on offer, and there's no wrong answer in how far you take treatment. When the time comes that comfort can't be held, our guide to the quality-of-life decision is there, and it leads gently into our End-of-Life space.

Before the fear runs away with you, hold onto this. Plenty of growths in the mouth are benign, and the gum is a common place for them. The old catch-all term was "epulis", and you may still hear it, though vets now name these lesions more precisely because they don't all behave the same (Today's Veterinary Practice, 2019). A peripheral odontogenic fibroma is genuinely benign and slow-growing, doesn't spread elsewhere and, unlike the ameloblastoma below, doesn't invade bone, and removing it completely usually settles it (VCA Hospitals, 2024; Today's Veterinary Practice, 2019). A canine acanthomatous ameloblastoma is also classed as benign and doesn't spread to other organs, but it is locally aggressive and digs into the surrounding bone, so it needs proper margins to stop it coming back (PetCure Oncology, 2024).

The reason all of this matters is the same reason it always does with lumps: you cannot tell which is which by looking, and neither can your vet. A sample is what tells you, and our piece on aspirates and biopsies explains how that's done. So a mouth mass is a reason to get a proper look and a sample, not a reason to assume the worst tonight.

If you've found a mouth change, the powerful move is the unglamorous one: book a look. The earlier a mouth tumour is sampled, the more options stay open, and for the benign ones it's often the end of the story. Whatever the result turns out to be, you'll be deciding from facts rather than fear, which is the best place to stand.