10 Nasty Dog Tumors Detectable on the Skin (Vet Approved)

While some tumors occur deep within the canine body and are impossible to detect visually, others can be discovered by pet owners during grooming, petting, or via simple observation. Don’t be alarmed and start looking at scary dog skin cancer pictures on the internet every time you find a new lump or bump. In most cases, a small red bump on dog skin can turn out to be a simple skin abnormality or a tumor that’s either benign or easily treatable.

If you do detect a weird growth, it’s very important to visit the vet to learn about the cause and if it needs to be treated. Below are some tumors that you might find by visually inspecting or touching your dog’s skin.

10. Mammary-Gland Tumors

These tumors are rarely found in unspayed females. However, if your dog is not spayed, these tumors are fairly common. In fact, the risk of mammary gland tumors in female dogs is higher than for women. According to the Veterinary Society of Surgical Oncology (VSSO), mammary gland tumors are so common that they account for 42% of all the tumors diagnosed in dogs, and about 23-34% of female dogs have a lifetime risk. 

The development of mammary glands has a direct relationship with these tumors. Only unspayed female dogs have fully developed mammary tissues, so they are at a higher risk of getting these tumors. On the other hand, female dogs that are spayed around 6 months of age are at lower risk because the ovaries are removed, so there's no estrogen production in the body to fully develop the mammary glands. The risks are higher for certain breeds and for dogs that become obese at an early age.

Diagnosis 

The usual symptoms of mammary gland tumors can vary from case to case. Some of the common ones are - 

• Swollen mammary glands
• Abdominal pain
• Discharge from one or more mammary glands
• Skin ulceration of the abdomen
• Unusual weakness and lethargy

The tumor can be detected by touch, can be large or small in shape, and they are most often located in the glands closest to a dog’s groin. Tumors that are attached to the skin often are cancerous, whereas tumors that can be moved by applying pressure are more likely to be benign. Weight loss has also been observed in dogs suffering from mammary tumors in the later stages. 

The tumors can be seen as swollen pea-sized growths on the mammary glands. Veterinarians will conduct a simple touch test and look out for abnormally hard swellings under the skin. They would decide whether the tumor is just under the skin or if it is attached to the mammary gland. If the tumor is benign, it is usually small and firm to touch and has a well-defined border. On the other hand, malignant tumors grow fast, so they are larger and usually have ragged edges. Malignant tumors also cause ulceration and inflammation. If the tumor is cancerous, the veterinarian will determine the mammary mass, the cancer stage, and if it has spread elsewhere. 

Veterinary oncologists would perform several tests to understand the stage and metastasis, which can include -

• Blood work that includes blood cell count, chemical panel, and clotting profile
• Urinalysis
• X rays
• Ultrasound or CT scan of the abdomen
• Fine needle aspiration (FNA) of the tumor and lymph nodes
• Biopsy and histopathology

Treatment

Surgery is usually the most effective treatment for mammary gland tumors, except for inflamed or metastatic cases. The veterinary surgeon will either remove the tumor or the mammary gland it is attached to, depending on the diagnosis. Usually, the entire mammary chain is not removed unless the diagnosis warrants it. 

Surgeons usually recommend spaying the female dog at the time of the surgery, but there’s some controversy regarding the recurrence of the tumor and whether that can affect the survival time of the affected dog. The only exception is secretory carcinoma because it depends on the production of estrogen in the body, so spaying is recommended along with surgery to stop the growth of the tumor and reduce the possibility of recurrence. The veterinary surgeons discuss this with the dog's parents at the time of diagnosis.

If the dog has mammary carcinoma, surgery is not recommended because it would not improve the chances of survival. In such cases, the oncologist would recommend radiation treatment along with the administration of nonsteroidal anti-inflammatory drugs (NSAIDs). Chemotherapy is only prescribed for cases where the cancer is in the advanced stages. 

The prognosis depends on several factors and varies from case to case, but the size of the tumor is the most important one. Larger tumors, measuring more than an inch and a half, tend to have a worse prognosis. Other factors that affect prognosis include ulceration, hydrologic grade, spread to lymph nodes, and metastasis. 

9. Testicular Tumors

Testicles that are enlarged, or the presence of one testicle that is larger than another, is often a likely tip-off to testicular cancer. If you notice any change in the shape of a dog’s testicles, get in touch with a vet for an examination. Note that dogs with undescended testicles are very likely to develop testicular cancer, so if that is the case with your dog, be vigilant to swelling of the descended testicle or your dog’s abdomen. Neutered dogs can’t develop testicular cancer.

There are the major types of testicular cancer found in dogs - 

• Seminoma tumors develop from the cells that produce sperm (germ cells)
• Interstitial cell tumors that develop from the cells that produce testosterone (Leydig cells)
• Sertoli cell tumors that develop from the cells assisting in sperm development (Sertoli cells)

There are other types of tumors that can develop from various cell types of a dog's testicles, but they are extremely rare. Male dogs that are not neutered have a higher risk of developing testicular tumors. 

Diagnosis and Treatment

Clinical signs are not always present in cases of testicular cancer and might be limited to the affected testicle. The vet might perform palpation of the scrotum to detect if the testicles are evenly sized, have nodular enlargements in them, and show signs of inflammation of the scrotum. 

Sertoli cell tumors can lead to hyperestrogenism, a condition where the tumors produce estrogen in the male dog’s body and cause signs of feminism that include enlargement of mammary glands and nipples, hair loss, and darkening of the skin (hyperpigmentation). The dog might also start squatting to urinate instead of raising its hind legs and show attraction to other male dogs. The condition can also affect the bone marrow and cause anemia and lethargy. 

If the tumor has turned malignant, clinical signs can appear depending on the organs affected by the tumor and can include weight loss, decrease in appetite, weakness, and vomiting. If the tumor has metastasized and affected the lymph nodes near the renal organs or prostrate, the dog might strain to urinate or defecate. 

Testicular tumors are usually detected during routine physical examination. The vet might notice an abnormal or missing testicle (that has gone back in the abdomen), and prescribe an ultrasound examination, followed by an abdominal surgery. The tumors are usually diagnosed post-surgery after the affected testicles are removed and sent for histopathology. 

For breeding males, veterinary doctors might go for additional tests instead of surgery to differentiate between tumors and less serious conditions like cysts. In such cases, they might start with an FNA. Testicular tumors have lower chances of spreading to the lymph nodes or other organs, and interstitial tumors usually don’t spread at all. But if there’s evidence of spread to other parts of the body, the veterinary oncologist might prescribe chemotherapy and/or radiation therapy, depending on the diagnosis. 

8. Mast Cell Tumors

One of the most common skin tumors in dogs, mast cell tumors are raised growths that appear on your dog’s skin. Tumors caused by mast cells are cancerous. Vets can determine if a lump on your dog’s skin is the result of mast cell growth through a needle aspiration of the lump.

Mast cells are found all over the body, and they release chemicals and compounds like histamine when they are exposed to allergens that cause sneezing, itching, and nose and eyes. Mast cell tumors are malignant and can form nodules or masses on the skin or other parts of the body, like the spleen, intestine, liver, or bone marrow. MCTs are the most common form of skin tumors diagnosed in dogs and about 85% of those dogs only develop one tumor. 

Mast cell tumors can also vary in appearance. They can also fluctuate in size suddenly and can grow bigger if they are agitated, causing degranulation. Mast cell tumor degranulation can release chemical compounds in the dog’s bloodstream, causing further complications like ulcers in the stomach or intestines and leading to symptoms like vomiting, lack of appetite, lack of energy, and black, tarry stool due to the presence of blood. These chemical compounds can also cause a less common but life-threatening allergic reaction called anaphylaxis.

MCTs are easily noticeable wart-like growths that are soft to the touch. There is usually one single growth in one area instead of a cluster of bumps. Only 11 to 15 percent of dogs have more than one MCT growth. However, they also go unnoticed often because they resemble insect bites or warts. Mast cell tumors are also extremely reactive and can aggravate suddenly due to palpation, causing degranulation. That’s why dog parents should get any skin anomalies checked immediately by a vet and refrain from feeling or pressing them. 

Diagnosis

MCTs are usually diagnosed using fine needle aspiration (FNA) or biopsy that determine how aggressive the tumor is, so the veterinary doctor can determine the best course of treatment. Tumors are graded from grade I to grade III, and they have a tendency to metastasize and spread to other parts of the body as the grade increases. The survival time for dogs with higher-grade MCTs is usually less than 4 months, whereas those with low-grade tumors tend to live for more than 2 years. 

Treatment

Low-grade tumors that have not spread to other parts of the body are usually treated with surgery, and chemotherapy is usually not required. A combination of surgery and chemotherapy is used to treat higher-grade tumors, even if they have not spread elsewhere in the body. They will undergo radiation therapy if surgery is not possible in the tumor location or if cancerous cells are present even after surgery. 

7. Histiocytoma

If you spot a bright red hairless bump on your dog’s skin, you may feel alarmed, particularly since histiocytomas often appear overnight. The good news is that histiocytoma tumors are benign. However, as with any bumps, it’s always recommended that you have a vet inspect and diagnose the issue.

Diagnosis

Painless and hairless bumps commonly occur on the ears, head, or legs. These bumps have a tendency to grow rapidly in the first month. Histiocytomas are usually found on the head, neck, ear, or limbs in the form of a small, hairless bump. Multiple masses are quite uncommon and are particularly found on Shar Peis. 

The lumps are usually less than 2.5 cm in diameter and may or may not be red in color and have ulceration. Cytology is usually the first step of diagnosis, but it may not yield definitive results. Veterinary doctors usually observe the regression of the mass and may conduct a complete histopathology after removing it to complete the diagnosis. 

Treatment

Histiocytoma tumors are rare tumors that might be eliminated by the dog’s immune system. However, there can be additional complications like ulceration, itching, secondary infections, or bleeding that may need to be treated using antibiotics or surgery. Usually, the condition is completely cured after surgery, although the vet might confirm that after the pathological analysis of the tumor and ensuring that microscopic cells are not left behind after surgery. 

6. Hemangiosarcoma

These cancerous tumors occur from blood cells, and they commonly appear in internal organs like the liver and heart. However, hemangiosarcoma can also occur on a dog’s skin. Most commonly, hemangiosarcomas on the skin will appear on a dog’s hind legs or neck or any body part that is hairless. They are very often red or black in color and can be treated with a combination of surgery and chemotherapy.

Hemangiosarcoma causes almost 66% of the tumors found in hearts and is extremely invasive, resulting in blood vessel fragmentation and rupture. Secondary malignant growths can also be found in the liver, lungs, bones, and adjoining lymph nodes. 

The cancer is often called a silent killer because it does not show any symptoms till the tumor enlarges and ruptures, which causes death. Hemangiosarcoma kills almost 300,000 dogs in the US each year, which is roughly 5-7% of the newly diagnosed cancer cases in the country every year. 

These tumors may not show any signs even when they are very large, and although some signs, like episodes of weakness, may occur repeatedly, they are so brief that they are often overlooked. There are no lab tests that can confirm the cancer unless the tumor is surgically removed and sent to a pathology lab. Sometimes, they appear as hard and dark-colored growths that usually occur on a dog’s hind legs. Tumors can change in size due to internal bleeding. These tumors do not cause skin ulcerations.

Treatment

If the veterinary oncologist cannot identify any metastasis, the dog might undergo aggressive chemotherapy and radiation treatment. However, these can amount to thousands of dollars and increase the life expectancy by about six months. 

5. Melanoma

Melanomas are dark brown or black in color and they look a lot like a mole. These marks can appear on the eyelids, nail bed, mouth, or skin. While some are benign, others are malignant, so it’s important to check in with the vet since appearance alone cannot reveal if the tumor is malignant or benign. Most benign melanomas appear on the skin, but those that appear in the mouth or in the nail bed can be malignant. Malignant melanomas can spread to the local tissues and underlying bones and even to other body parts like the liver or the lung. 

The majority of melanomas present on the skin or in the mouth look like raised masses and tend to be dark, although some may appear pinkish. If the melanoma appears in the mouth, clinical signs include drooling, bad breath, pain, bleeding, and difficulty holding food in the mouth. Tumors that appear on the digits/nail beds can cause infection and swelling in the toes or toenails and even cause lameness in the affected leg. 

Diagnosis

Melanomas are usually diagnosed using FNA or biopsy, and the oncologist may conduct further tests like FNA of the lymph nodes, X-rays, and ultrasound to determine how much the tumor has spread to other parts of the body. Blood and urine tests are also conducted initially to determine the dog’s overall condition and course of treatment. CT scans and MRIs can also be done to understand exactly how much the tumor has spread. 

Treatment

Veterinary oncologists usually conduct surgery combined with radiation therapy and systemic treatment. If the tumor is recurrent or inoperable, the oncologist might prescribe palliative radiation therapy to slow down the growth of the tumor or shrink it. Chemotherapy has limited efficacy for melanomas, with an average response rate of about 30%. There have been recent advances in the development is a vaccine called Oncept that stimulates the immune system to target the growth of melanoma tumor cells in the dog’s body with minimal side effects. 

4. Lipoma

These fatty skin tumors are benign and appear in the subcutaneous layer of a dog’s skin. These tumors have a soft feel and can be moved by applying pressure. The malignant form of these tumors is called liposarcoma. Lipomas should not be confused with lymphomas that are found in the lymph nodes and are quite dangerous. 

Lipomas are usually soft lumps underneath the skin that move ever so slightly when touched. These lumps are usually seen occurring under the armpits, neck, or belly. Even though lipomas are benign, they can grow big and cause pain. They can vary in shape and size, ranging from round to oval, and can be less or more bulging. Some are squishy, while others are firm to touch, and they may or may not be connected to surrounding tissues. 

Treatment

These tumors are usually surgically removed unless the vet decides to wait and watch its growth. There are also chances of lipomas or liposarcomas recurring after surgery, so the oncologist might surgically remove them again and prescribe radiation therapy afterward. If the vet decides to monitor the growth, the pet parent would be asked to record the growth, changes in shape, and firmness of the tumors. The vet might also prescribe a specialized diet to control the dog’s weight, as some lipomas tend to shrink after weight loss. 

3. Basal Cell Tumors

These tumors are quite common in dogs. Oftentimes, a single basal cell tumor is seen as opposed to multiple growths. The size of the tumors varies between 0.2-10 centimeters, and they are usually hairless and raised above the skin. You’ll spot these tumors on a dog’s neck or shoulders as dome-shaped, hairless masses. Generally, they are not malignant and can be surgically removed. However, sometimes, they can also be mistaken for basal cell carcinomas, which is the malignant form of these tumors. Basal cell tumors may ulcerate and can thus be painful. 

Basal cell tumors can cause multiple symptoms, such as -

• Itching
• Inflammation
• Pain
• Bleeding
• Ulceration
• Pus

Diagnosis

First, a cytological examination is conducted using FNA. If the test is inconclusive, it might be followed by a biopsy for confirmation. The biopsy can also determine if the tumor is benign or cancerous. About 10% of basal cell tumors tend to be cancerous. 

Treatment

The veterinary doctor will prescribe an appropriate treatment depending on several factors, such as -

• Size 
• Location
• Stage
• Depth 

If the lesion is growing or causing discomfort, the oncologist will prescribe surgery. However, if the tumor is not growing or causing any discomfort, it can be left as it is and monitored. These tumors can grow slowly over time if they are not removed and can cause itching, bleeding, swelling, or ulceration, so they may be removed with surgery later. 

2. Squamous Cell Carcinoma

These tumors are a result of sun exposure and generally occur in hairless areas on your dog’s skin. They appear to have various different colors, including red, white, or gray. More often than not, these tumors are malignant and thus need surgical intervention. These sores occur in areas with light-colored fur or places where there is no hair. The growths are usually flaky and prone to bleeding. Growths can occur on the nose, scrotum, legs, nail beds, paw pads, or ears.

SCC usually appears as a solitary mass on the skin. However, there is another rarer form of the disease called multicentric squamous cell carcinoma that can appear as two or more lesions in multiple locations. This condition is also called Bowen’s disease or Bowenoid carcinoma. 

SCC lesions are usually found in the light-skinned areas of the dog’s body and usually look like irritated or ulcerated skin. Lesions on the toes or nail beds can be worse and often cause bleeding or even loss of toenails. Lesions in other parts of the body can also become dry, itchy, and bothersome. The dog should not be allowed to scratch or bite that area. 

Diagnosis

The first step is FNA, followed by a biopsy if the results are inconclusive. Histopathology can help the oncologist understand how the tumor might behave. When it appears on the skin, metastasis to nearby lymph nodes is uncommon, but it might happen. SCC on the nose can spread to the lymph nodes under the chin. Multicentric SCC can recur in new places even after surgical removal of the tumors. 

SCC in the digits is often more aggressive than the rest and can spread to lymph nodes and even other parts of the body. The veterinary oncologist might determine the stage of the cancer with supporting tests like blood tests, urinalysis, X-ray, and ultrasound. 

Treatment

SCC on the skin is usually treated with surgery, as radiation therapy is not very effective. However, surgery might be followed by radiation therapy if the surgery fails to remove the tumor completely. SCC on the digits also needs to be surgically removed, but that might be more extensive than just removing the tumor and can sometimes require amputation of digits or even limbs. The efficacy of chemotherapy is controversial and best discussed with the veterinary oncologist. Multicentric SCCs are usually removed surgically, along with immune response modifiers. 

1. Lymphoma

Also known as lymphosarcoma, this cancer of the lymph nodes has more than 30 classification types. Multicentric lymphoma is the most common variety of tumors in dogs. It’s characterized by swollen glands in the dog’s neck. Although there is no cure for lymphoma, chemotherapy can be used to reduce symptoms and extend a dog’s life. There are four common types of lymphomas -

• Multicentric lymphoma is the most common type (85% of cases) and affects the lymph nodes first. 
• Alimentary lymphoma, also called gastrointestinal lymphoma.
• Mediastinal lymphoma is rare and can affect the chest
• Extranodal lymphoma mostly occurs on the skin (cutaneous lymphoma) but can also appear in other parts of the body. 

Multicentric Lymphoma tumors typically have a rubbery texture, and they move freely under the skin. They can cause multiple symptoms like - 

• Lack of appetite 
• Lethargy
• Weight loss
• Swelling
• Unusual thirst
• Frequent urination
• Diarrhea 
• Vomiting
• Trouble breathing

Diagnosis 

Lymphoma is usually diagnosed with FNA and biopsy, but sometimes, the vet might have to surgically remove a large part of the lymph node or an affected organ for histopathology. 

Treatment

Lymphoma is usually treated with chemotherapy administered orally or through an IV channel, or a combination of both. Dogs may have to go through the treatment for several months. Sometimes, a dog might build drug resistance to one type of chemotherapy drug, so the vet might prescribe treatments to reverse the drug resistance. The dog may go into partial or total remission, but that rarely cures the disease. Lymphoma usually always comes back and can be harder to treat as the cancer cells become resistant to chemotherapy drugs. 

Dog Skin Cancer - When Is a Tumor Malignant?

Skin tumors are the most common tumors found in dogs. Some breeds, such as Boxers and Retrievers, are at a higher risk of having a skin tumor in their adult or senior years. Dog skin cancer is not always a given, though. Tumors may be benign (non-spreading or non-cancerous) or malignant (cancerous), but any lump should be looked at by a veterinarian. Not all skin tumors may be caused by the sun, but sun exposure can increase the chances of developing tumors, especially if your dog has light-colored fur. Areas that aren't covered by fur, like the nose and paw pads, are at greater risk of sun damage. You can take some steps to help prevent it, but the best defense against skin cancer is early detection, so talk to your vet immediately after finding any lumps.

Is it dog skin Cancer?

Certain skin problems can be mistaken for skin cancer. Some of them can be just as serious as cancer, so any questionable lump or growth should be examined and treated.

• Benign Tumor: Sometimes tumors are not cancerous, but they may still need to be removed.
• Fungal Infection: Ringworm and blastomycosis can cause skin lesions or significant irritation. Ringworm is highly contagious, and blastomycosis can cause significant lung damage, so it is important to treat the infection as quickly as possible.
• Allergic Reaction: Some allergic reactions, such as eosinophilic granuloma (although rare for dogs), can cause raised ulcers, especially on the mouth, face, feet, and thighs.

If a tumor seems to be growing or is an open wound that isn't healing, it’s more likely that the tumor is cancerous. Either way, make sure to have every tumor examined by a vet. They’ll be able to give you an exact diagnosis with a biopsy and other lab tests and will likely recommend surgical removal and additional treatment, especially if the tumor is malignant.

Most Common Types of Skin Tumors in Dogs

Several skin tumor types are commonly found in dogs, and their prevalence has allowed vets to develop specialized treatments to best extend length and quality of life. If detected and removed early, some dogs can recover completely from some kinds of skin tumors. Other tumors may require more aggressive treatment, which can become very expensive.

• Mast Cell Tumors: Mast cell tumors are the most common malignant tumors for dogs and are usually solitary lumps found on the body or legs. Breeds that are at risk include Beagles, Boston Terriers, Boxers, Labrador Retrievers, Pugs, and Schnauzers. One strange side effect of the tumor is an increase in stomach acid and the likelihood of developing gastric ulcers. Since these tumors spread easily, vets will often start with surgical removal, but the use of radiation and chemotherapy has also been used to fight mast cell tumors.
• Basal Cell Tumor: This form of tumor is one of the most common in animals and among dogs and is often found in Cocker Spaniels and Poodles. These tumors grow from deep skin layers and can be seen as a single hairless lump on the head, neck, or shoulders. It is unlikely they will be malignant, and there is a low risk of spreading, so after freezing or surgical removal, many dogs recover completely.
• Melanoma: Melanomas are often seen as a darkened area, sometimes looking like an overgrown or raised mole. They can be found on the mouth or mucous membranes or in areas with hair -- even in the toes of black dogs. Melanomas grow very quickly, especially with sun exposure or licking, and can easily spread to the lungs and liver if not treated quickly. More than some other, slower-growing tumors, melanomas are likely to require radiation or chemotherapy in addition to surgical removal.
• Squamous Cell Carcinoma: This tumor is usually firm and raised, sometimes mistaken for a wart, and found on the abdomen or genitals. Basset Hounds, Beagles, Bull Terriers, Collies, Dalmatians, Keeshonds, Schnauzers, and other dogs with short coats are at risk. This tumor has been linked to sun exposure and possibly also the papillomavirus. While it is unlikely to spread to organs, it can still cause significant damage to surrounding tissue.
• Hemangiosarcoma: This malignant tumor grows from blood cells, appearing as a raised, bruised lump (or multiple lumps) on the hind legs or abdomen. The lumps may change in size or color but are often firm and malleable. Boxers, English Setters, German Shepherds, Golden Retrievers, Pit Bulls, Whippets, and older dogs are more likely to have hemanglosarcoma. These tumors are more likely to metastasize (spread to new areas or organs), and sun exposure for light-colored dogs may have a predisposition to getting hemangiosarcoma. This tumor will require surgical removal and probably ongoing radiation therapy because it is so aggressive. Unfortunately, it usually shortens a dog's lifespan.

Frequently Asked Questions

What does a cancerous lesion look like on a dog?

What does a cancerous spot look like?

What does canine melanoma look like?

How do you tell if a mass on a dog is cancerous?

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This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.