3 Types of Tumors Often Found on a Dog’s Lips

This article was updated on August 26th, 2023

Finding a new lump on your dog’s lip is upsetting.  Your pooch’s perfect face is altered and your probably worried.  What is this new lump and how will it affect your dog’s health? Working as a veterinary technician in both general practice and a large specialty hospital for the past 30 years, I have seen a lot of lumps and answered a ton of questions about them. What a lot of people want to know is:

What are these lumps?  What causes these lumps?

The lumps and bumps you may find on your dog’s lip have many causes. 

Some lumps (referred to medically as masses) may start with a minor injury, a scratch or a bug bite that allows bacteria to enter the skin.  This can result in pustules which are little pockets of pus or it may start an inflammatory response or allergic reaction disrupting the skins normal growth.

Some lumps are viral in origin.

Lumps or masses that are a result of an abnormal overgrowth of cells are considered neoplastic tumors.  A neoplastic tumor can be benign (not cancerous) or malignant (cancerous).  Some neoplastic tumors develop due to hormonal changes in the body.  Many develop for unknown reasons. 

Genetics play a part, some dogs may be predisposed to certain tumors. Environmental influences and diet are considered possible factors in tumor growth.

Canine oral tumors are fairly common, both benign and malignant.  Included under the scope of “oral tumors” are lumps found on the dog’s lip.

One important thing for a dog owner to know is that any lump or bump you find on your dog’s lip or elsewhere has the potential to be cancerous.  The only way to know for certain that a lump (mass) is benign is to take a sample of it and have the sample examined microscopically. 

This doesn’t mean that every lump found on your dog needs to be sampled.  Your veterinarian can examine a lump, do a basic wellness exam, take a history and then make a well informed decision regarding the lump and how to proceed.  Sometimes a valid treatment plan can be initiated without any samples being taken.

Malignant masses and tumors often found on a dog’s lip

Oral malignant tumors are more prevalent in male dogs than females.  They occur mostly in older dogs.  Some of them are very aggressive and carry a poor prognosis if not caught early.

When the tumor is in the mouth as opposed to on the lip, they can be more problematic,  They can be fairly extensive and interfere with the usual function of the mouth.  The affected dog

may have trouble swallowing.  You may notice excessive drooling or bad breath.

Lumps on the lip are not typically painful, unless they ulcerate or become infected.  When these tumors become more extensive inside the mouth they can become painful.

If you think that your dog is painful your veterinarian can prescribe an appropriate pain medication for your particular situation.

1. Oral malignant melanoma

Oral malignant melanoma is the most common of the malignant oral tumors.  It occurs most often in dogs greater than 10 years old.  It is an aggressive tumor that invades the tissue surrounding it as well as spreading to the lungs.

The lump or tumor will be a red or black nodule that may ulcerate or bleed. Complete excision is necessary.  Sometimes chemotherapy or radiation therapy are recommend after surgery.  Unless caught early this cancer is a challenging one to treat and carries a poor long term prognosis.

Cocker spaniels, German shepherds, Golden Retrievers and Miniature poodles seem prone to this tumor.

2. Mast cell cell tumor

Mast cell tumors can grow on the lip.  They may be red and swollen.  Mast cell tumors are tricky, they can be very nondescript and look quite innocent, or they can be red, inflamed, ulcerated and ugly. The disease may be isolated to the lip, occasionally the spleen, liver, intestines or bone marrow can be affected.

Any dog is at risk for mast cell tumor, but Boxers, Bull Terriers, Boston Terriers and Labrador Retrievers are prone to them.

They can grow slowly or quickly and they do metastasize (spread).  Treatment and prognosis depend on the advancement and spread of the tumor.  They are graded I-III with grade I tumors carrying the best prognosis.

For less advanced disease surgery can give a very good longterm prognosis.  Higher graded tumors may require chemotherapy after surgery and the prognosis is not as good.  Predisposed breeds have a higher risk of metastasis.

When mast cell tumors are handled or manipulated, they can “degranulate” which causes them to become red, inflamed and itchy.  It is best to leave them alone until your vet appointment and make sure your dog isn’t licking or biting at them.  If you suspect a mast cell tumor have it seen by your veterinarian as soon as you can as they can progress fairly quickly.  For a more in depth look at the reactive behavior of mast cell tumors please click on this link or view more pictures of mast cell tumors in dogs with our veterinarian team’s explanations.

3. Squamous cell carcinoma and fibrosarcoma

These two types of malignant tumors do not commonly occur on the lip. They are both locally invasive and sometimes require surgical removal of part of the bony jaw as well as subsequent chemotherapy or radiation therapy.

Although not often seen on the lip it is important to diagnose your dog’s lip mass to ensure it is not one of these aggressive tumors.   

4. Other tumors, lumps and bumps on a dog’s lips

If you have noticed a new lump or bump on your dog’s lips, you are probably jumping to all sorts of conclusions about what it could be.

Related post: Common Bumps on a Dog’s Lips.

What do I do about the new lump I found on my dog’s lip?

Any lump you find on your dog’s lip should be checked by a veterinarian.  The question is really how quickly you need to get your dog in to be seen.  

Oral masses (including lip masses) in dogs under the age of two are usually benign.  So for dogs in this age group waiting  a week or two before seeking veterinary care for a mass on the lip is a valid option.  There is a chance the lump will go away on its own.

This is of course if the lump is not bothering your dog.   If the lump is red or inflamed,  is bleeding or oozing pus or fluid or has a foul odor you should bring your pooch to the vet as soon as possible.

Ulcerated lumps and lumps that grow rapidly should be seen right away.

If your dog has had cancer in the past, or it is known that your dog’s genetic line is predisposed to cancer, they should be seen quickly.

Some of the malignant (cancerous) oral tumors can be very aggressive and spread quickly.  Because of this your better off seeing your vet as soon as you can.  If the lump is cancer the sooner treatment is started the better the chance for a good outcome.

There is nothing that you can do at home to shrink the tumor on your dog’s lip, 

Lumps of the lip are not typically painful.  If you think your dog is painful consult your veterinarian so that they can recommend or prescribe a pain killer for your dog.

Related post: Dog with Red & Swollen Lips