LUMPS & BUMPS: What are they and should I worry?

Karen Helton Rhodes, DVM, DACVD

Terri Bonenberger, DVM, DACVD

Your dog’s veterinary dermatologists!

Dogs can have skin tumors just like people.  Canine skin is also subject to sun-induced skin problems and tumors, just as recognized in people. Some of these masses (lumps and bumps) are cause for worry while others are harmless.  The trick is figuring out how to tell “which is which”! 

How can you tell if you should worry?

Your veterinarian can help put your mind at ease.  Remember that just looking at a mass or palpating the mass is not an accurate assessment….even for the experienced eye.  Your veterinarian can get an idea if the lump is worrisome BUT will need to run some diagnostics to give you a more accurate answer.  A simple cytology can give you a quick and easy answer in many cases.  Your veterinarian will insert a small needle/syringe into the center of the mass and pull back on the plunger to attempt to extract some cells.  That small drop of cells is then placed on a glass slide and viewed under the microscope.  All of this can be done in the exam room without the dog even getting upset or worried.  You can have your answer is a few minutes wait time!  Keep in mind that some masses do not shed cells very easily during a cytology procedure.  In those cases, a biopsy is necessary for an accurate answer.  A biopsy is ALWAYS the most definitive route to an accurate answer.  Cytology can simply be a shortcut in some cases.

One of the most common lumps seen in dogs in my clinical practice is the Lipoma- this is a fatty mass located in the subcutaneous tissue under the skin.  These can be small or huge.  They can be single or multiple. They can often be felt rather than seen and are soft and moveable. They are NOT typically a problem unless they inhibit movement such as under the leg.  These tumors can be easily “diagnosed” with a quick cytology in the exam room.  Cytology with yield a fatty substance that is easily identified. These lumps are in the category of “don’t worry”.

All cancers are not created equal!

Some quick semantics to make conversing with your veterinarian easier:

1.  Lumps & Bumps:  used to describe a raised nodule that could be either inflammatory or neoplastic

2.   Tumor or Neoplasia:  Term often used for a mass that is due to an abnormal overgrowth of cells (cells out of control).  It does not indicate if the neoplasm/tumor is benign or malignant.

3.  Benign tumor: The proliferative overgrowth of cells in the tumor lacks the ability to spread or invade other tissue.  The cells are relatively normal in appearance, as opposed to malignant cells which can appear to be rather bizarre.

4. Malignant tumor or Cancer:  Indicates that the abnormal overgrowth of cells creating the mass has the potential to invade and spread to other parts of the body.



There are many skin tumors recognized in the dog.  Each tumor type could be the entire subject of an individual article.  Look for future entries on individual tumor categories. This article serves as a brief overview of some of the more common tumors seen in the dog.

Let’s divide the skin tumors into two simplistic categories: 

sun-induced & not sun-induced

1st category:  Common Sun Induced (Actinic) Dermatoses in dogs

Ultraviolet Light (UVA & UVB) can cause a spectrum of actinic (solar) dermatitis in dogs to include non-neoplastic, pre-neoplastic, and neoplastic lesions.

1.  Sunburn leading to Actinic keratoses: Many dogs love to sunbathe.  Those with light pigmented skin are most at risk.  Repeated sun exposure can cause permanent damage with scarring, pigment change, comedones (dilated hair follicles), and furunculosis (ruptured inflamed hair follicles).  You can also see large hemorrhagic bullae (blood blisters). The skin can sometimes become rough and thickened to the touch. These lesions can be considered pre-neoplastic.  The cellular dynamics are changing due to repeated UV exposure.

photo courtesy of Dermatology for Animals
Actinic (solar) Keratoses

2.  Tumors caused by chronic sun exposure

*Squamous Cell Carcinomas

*Hemangiomas (benign)

*Hemangiosarcomas (malignant) 

Your skin is constantly changing and subject to environmental insult such as UV light.


Squamous Cell Carcinomas

80% of these tumors arise from chronic actinic keratosis (chronic sun exposure).  These tumors are often crusted and ulcerated and tend to be most common in lightly pigmented regions.  These tumors do not tend to spread to distant parts of the body but they can be very invasive locally and they can erode local blood vessels.

squamous cell carcinoma of the groin

(note the red crusted lesions)

advanced squamous cell carcinoma on a cat’s ear

Hemangiomas and Hemangiosarcomas

Hemangiomas are considered benign while hemangiosarcomas are malignant.  As a quick tip:  “omas”  are typically benign and “sarcomas” are malignant.  Luckily, hemangiomas are more common than hemangiosarcomas.  These tumors are well demarcated, red nodules.  They may be single or multiple.  These tumors are centered around blood vessels….thus their red color.  The malignant form (hemangiosarcomas) do not tend to be very aggressive in spreading to distant regions (metastasis) but have that potential.







2nd category: Tumors of the skin not induced by sun exposure

Basal Cell Tumors:

These tumors are primarily benign solitary nodules 1-10cm in diameter. They may be pigmented or even ulcerative.  These nodules are often found on the head but may occur anywhere on the body.  Luckily, even the malignant forms are slow growing and rarely metastasize(spread to other regions).  

Sebaceous Gland Tumors

The most common forms are Sebaceous Gland Adenomas.  They look like small warts on the skin and the dog may actually have many.  Older dogs tend to get them most frequently. They may occur anywhere on the dog and are often traumatized by grooming.  They can secrete a waxy yellow substance that will accumulate along the surface and mat the hair.  It is rare that they cause a problem in that the malignant form is uncommon.



DO NOT PANIC!  85% of Melanomas in the dog are benign.  They may be pigmented but the converse is also true.  This can complicate a visual diagnosis.  The benign forms are typically flat brown patches or raised dome shaped nodules less than 2cm in diameter.  The malignant forms are rapidly growing masses that are usually greater than 2cm in diameter.  Keep in mind that these are generalizations!  

                                                                                        pigmented plaque: melanoma     

                                                                                    pigmented plaque: melanoma


Hair Follicle Tumors

These tumors are often cystic in nature and have a central pore filled with thick cheesy material.  Most are benign.

Mast cell Tumors

These tumors arise from mast cells. These tumors can arise from the skin, spleen, or even the gastrointestinal tract.  Mast cells contain histamine and other vasoactive amines that can cause swelling and erythema (redness).  Skin mast cell tumors are categorized as Grade I (benign), Grade II (intermediate), and Grade III (malignant).

Interestingly, these tumors may appear and then disappear. They may appear as solid nodules or be rather spongy in character.

                                                                                      spongy nodule on the toe

                                                                                      spongy nodule on the toe

Histiocytic Tumors

These cells (histiocytes) are involved in some unusual diseases that are considered proliferative and not neoplastic:  Cutaneous Histiocytosis, Systemic Histiocytosis, and Malignant Histiocytosis.

There are two tumors of histiocytic origin:  histiocytomas and histiocytic sarcomas. The histiocytoma is very common as a benign solitary single small nodule of young dogs that often regresses spontaneously!

The histiocytic sarcoma is a rare malignant rapidly growing tumor. 


This complicated group of neoplasms is rather varied.  These lesions can look nothing like tumors and appear as dry hairless scaly patches or, more typical, as large groups of nodules as well as enlarged lymph nodes. 

                                                                         Scaling patch- cutaneous lymphoma

                                                                         Scaling patch- cutaneous lymphoma

                                                                     multiple lymphoma nodules around the muzzle

                                                                     multiple lymphoma nodules around the muzzle

As you can see from the photos, making a visual diagnosis is VERY difficult.  Diagnostics are always necessary: cytology and/or biopsy are needed for an accurate answer.

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