Oral Cancer in Dogs and Cats: Lumps, Drooling and Diagnosis

The mouth is the fourth most common site for cancer in dogs and cats, harbouring several distinct tumour types with vastly different behaviours and prognoses. Understanding which type your pet has been diagnosed with is essential for making informed treatment decisions.

"Oral tumours are among the most challenging cancers we treat because they affect eating, drinking, and breathing — the most fundamental functions. But modern surgical techniques allow us to remove even large portions of the jaw while preserving excellent quality of life." — Dr. Sarah Chen, DVM

In dogs, malignant melanoma is the most common oral tumour, accounting for 30 to 40 per cent of oral cancers. Despite the name, oral melanomas in dogs are frequently non-pigmented (amelanotic), appearing as pink or red masses rather than the dark lesions people associate with melanoma. They are highly aggressive, with a strong tendency to invade bone and metastasise to lymph nodes and lungs. Squamous cell carcinoma (SCC) is the second most common oral tumour in dogs and the most common in cats. In cats, oral SCC is devastatingly aggressive, often invading the jawbone and being diagnosed at an advanced stage. Fibrosarcoma is the third most common oral tumour in both species — locally invasive but slower to metastasise than melanoma or SCC.

Less common but worth mentioning is acanthomatous ameloblastoma (previously called acanthomatous epulis) in dogs — a locally aggressive tumour that destroys bone but very rarely metastasises, making it highly curable with adequate surgery. Proper identification of the tumour type through biopsy is the essential first step in planning treatment.

Oral cancer in pets often goes undetected in its early stages because most owners don't regularly look inside their pet's mouth. By the time symptoms become obvious, the tumour may be advanced. Knowing the warning signs and performing periodic oral checks can make a life-saving difference.

Persistent bad breath (halitosis) that worsens progressively is one of the earliest signs. While bad breath can result from dental disease, a sudden change in breath odour — particularly a sweet, necrotic, or unusually foul smell — warrants investigation. Good dental care habits make it easier to notice when something has changed. Excessive drooling, especially if the saliva is tinged with blood, is another key warning sign. Dogs may drool from one side of the mouth if the tumour is causing pain or obstruction on that side.

Difficulty eating — dropping food, chewing on one side, reluctance to eat hard food, or outright refusal to eat — often signals pain from an oral mass. Cats may stop grooming themselves, leading to a matted or unkempt coat. Facial swelling can indicate a tumour that has invaded the jawbone, causing visible asymmetry of the face or muzzle. Loose teeth in an otherwise healthy mouth can be an early sign of bone-invasive oral cancer — if a tooth becomes loose without obvious dental disease, the underlying bone should be evaluated.

Other signs include pawing at the mouth, bleeding from the mouth or nose, a visible mass on the gums or palate, nasal discharge, and general signs of pain or discomfort such as reluctance to have the head touched, hiding, or behavioural changes. Weight loss due to decreased food intake is common in advanced cases. Any of these signs persisting for more than a few days deserves a veterinary examination.

Oral cancer has a particularly poor track record for early detection, and several factors conspire to delay diagnosis. The most fundamental issue is that the oral cavity is simply not a place most pet owners inspect regularly. Unlike skin lumps that are discovered during petting or grooming, oral masses grow hidden from view. Many pets — especially cats — actively resist having their mouths examined, making casual oral checks difficult.

Pets are also remarkably adept at compensating for oral discomfort. Dogs and cats with significant oral pathology often continue to eat (switching to softer foods or swallowing kibble whole) and behave relatively normally until the tumour is quite advanced. The survival instinct to continue eating is strong, and many owners are reassured by a pet that is 'still eating fine' — not realising that the animal is eating despite considerable pain rather than in the absence of it.

Early oral tumours can also be misidentified. A small gingival mass may be mistaken for an epulis (a benign gum growth), a dental abscess, or generalised gingivitis. Loose teeth caused by tumour invasion of the jawbone may be attributed to periodontal disease. Blood-tinged saliva might be blamed on a chew toy injury. Without biopsy, these misattributions can delay diagnosis by weeks or months — a significant timeframe for aggressive tumour types.

This is why regular veterinary check-ups that include a thorough oral examination are so valuable, particularly for senior pets. Dental procedures performed under anaesthesia also provide an opportunity for a complete oral examination that is impossible in an awake patient. Veterinarians are trained to recognise subtle tissue changes that may indicate early neoplasia — swellings, colour changes, asymmetry, or areas of abnormal texture. Asking your vet to pay special attention to the oral cavity during wellness visits is a simple but powerful step toward earlier detection.

A comprehensive oral examination typically requires sedation or general anaesthesia, as a thorough assessment of the entire oral cavity — including the back of the throat, the underside of the tongue, the hard and soft palate, and the tonsils — is virtually impossible in an awake patient. This is particularly true for cats, whose smaller mouth and lower tolerance for handling make conscious oral examination extremely limited.

During the examination under anaesthesia, the veterinarian will assess the size, location, and appearance of any masses, check for bone involvement by probing and palpating the jaw, and evaluate regional lymph nodes (submandibular and retropharyngeal). Dental radiographs or, ideally, a CT scan of the head are essential for determining whether the tumour has invaded bone. CT imaging is considered the gold standard for staging oral tumours because it provides three-dimensional detail of bone involvement, tumour extent, and lymph node size that conventional X-rays cannot match.

A biopsy is absolutely essential — there is no substitute for histopathological diagnosis. Incisional biopsy (removing a representative piece of the tumour) is preferred over fine needle aspirate for oral masses because the tissue architecture is important for determining tumour type and grade. The biopsy should be taken from the margin between tumour and normal tissue, avoiding necrotic central areas that may not yield diagnostic material.

Complete staging includes three-view chest X-rays or chest CT to check for lung metastases, fine needle aspirates of regional lymph nodes, and complete blood work. For malignant melanoma in dogs, additional staging may include abdominal ultrasound, as melanoma can metastasise to abdominal organs. The staging results, combined with the biopsy diagnosis, determine the treatment plan and provide a realistic prognosis for your pet.

Surgery is the primary treatment for most oral tumours and can be remarkably successful when performed by an experienced surgeon. Mandibulectomy (removal of part of the lower jaw) and maxillectomy (removal of part of the upper jaw) sound alarming, but dogs and cats tolerate these procedures far better than most owners expect. Up to 50 per cent of either jaw can be removed while maintaining good function — pets continue to eat, drink, and even carry toys. Cosmetic results, while not perfect, are generally acceptable, and most pets adapt within two to four weeks.

For acanthomatous ameloblastoma in dogs, surgery alone with adequate bone margins achieves cure rates exceeding 90 per cent. For oral melanoma, aggressive surgical excision is combined with adjuvant therapy — the canine melanoma vaccine (Oncept) is a notable advancement. This DNA-based vaccine stimulates the dog's immune system to recognise and attack melanoma cells. Studies have shown it can extend median survival times from 5-6 months (surgery alone) to 18 months or more when combined with local tumour control.

Radiation therapy plays an important role for tumours that cannot be completely excised surgically or as an adjunct to surgery with narrow margins. Definitive radiation protocols (multiple small fractions over several weeks) offer the best long-term local control. Palliative radiation (fewer, larger fractions) can provide significant pain relief and tumour shrinkage for patients where cure is not achievable.

For feline oral squamous cell carcinoma — the most challenging oral cancer — treatment options are unfortunately limited and outcomes remain poor despite ongoing research. Surgery is often not possible due to the tumour's location and extent at diagnosis. Radiation provides temporary relief in some cases. Chemotherapy (piroxicam, carboplatin) has shown modest benefit. Palliative care focused on pain management and nutritional support is an important and valid choice when curative treatment is not feasible. Research into targeted therapies and immunotherapy for feline oral SCC continues and may offer improved options in the future.

One of the greatest barriers to treating oral cancer is the fear that jaw surgery will destroy a pet's quality of life. This concern is entirely understandable but largely unfounded for the majority of patients. Decades of veterinary surgical experience and multiple quality-of-life studies have consistently shown that dogs and cats adapt remarkably well to partial jaw removal.

After mandibulectomy or maxillectomy, most pets begin eating soft food within 24 to 48 hours of surgery. The tongue may deviate slightly toward the surgical side, and some dogs experience temporary drooling, but these issues typically resolve or become manageable within a few weeks. Dogs that have undergone rostral mandibulectomy (removal of the front of the lower jaw) may have a tongue that protrudes slightly — a cosmetic change that rarely bothers the dog and that owners usually find endearing rather than distressing.

Owner satisfaction surveys following jaw surgery in pets consistently report high satisfaction rates — typically 85 to 95 per cent of owners would choose the surgery again. The key factor in this positive assessment is pain relief: removing a painful oral tumour dramatically improves the pet's comfort, appetite, and demeanour. Pets that were withdrawn, reluctant to eat, and visibly uncomfortable before surgery often return to their normal personalities within days of the procedure.

Post-surgical care includes a period of soft food (typically two to four weeks), oral rinses to keep the surgical site clean, pain medication, and restricted activity during healing. Long-term, most pets return to a completely normal diet including dry kibble. Regular follow-up appointments are essential for monitoring the surgical site for recurrence and checking for metastatic disease. With appropriate treatment and monitoring, many pets with oral cancer enjoy months to years of good quality life — a testament to the resilience of our companion animals and the advances in veterinary surgical oncology.