Are black moles on dogs cancerous

By Isabella Storyclaire

last updated September 16, 2024

Contributions sourced from

Dog Skin Cancer: Types, Symptoms, and Treatment

The word cancer instills fear into the heart of every dog owner, but not all growths are cancerous. The most common growth found on dogs are lipomas, which are fat cells. Also commonly found on dogs are sebaceous cysts, which can become cancerous. If your veterinarian has diagnosed your dog with skin cancer, or if you are concerned that your dog might have a cancerous skin tumor or lump, it is understandable to feel worried and fearful.

Your veterinarian is your best resource to help you through any questions you may have about your dogs health and skin issues. However, here is some information you need to know about skin cancer in dogs to help you understand your dogs possible condition.

Can Dogs Get Skin Cancer?

Dogs can get skin cancer, just like we can. In fact, skin tumors are the most commonly diagnosed type of tumor in dogs. This is partly because skin tumors are easier to see with the naked eye than other types of tumors, and partly because the skin is exposed to more of the environmental factors that can cause tumors, such as chemicals, viruses, and solar radiation, then your dogs internal structures. Luckily, this also means that you and your veterinarian have a better chance of catching your dogs cancer before it progresses past available treatment options.

Causes of Skin Cancer in Dogs

Skin cancer can have a variety of causes. Just like with people, genetics play a large role in which dogs are more likely to get skin cancer. In fact, it is believed that genetics are the number one factor in the risk of a dog getting skin cancer. Triggers that may lead to a dog developing skin cancer include too much exposure to the sun, chemicals in the environment, hormonal abnormalities, and certain types of viruses.

Types of Skin Cancer in Dogs

There are several different types of skin cancer in dogs, just like there are several different layers of the skin. Each layer and skin component can develop distinct tumors, some of which may turn out to be cancerous.

Some of the more common types of skin cancer in dogs are:

Malignant melanoma
Mast cell tumors
Squamous cell carcinoma
Histiocytic cell tumors
Fibrosarcoma

Malignant Melanoma

Melanomas can be either malignant or benign. These tumors are often dark-pigmented or can lack pigment. While benign melanomas are more common, malignant melanomas are a serious concern, as they grow quickly and have a high risk of metastasis (spreading to other organs).

Malignant melanomas are most commonly found on the lips, mouth, and nail beds. According to some researchers, the head, neck and scrotum areas are also moderately predisposed to skin cancer. Certain breeds, for example Miniature and Standard Schnauzers and Scottish Terriers, are at an increased risk, and males appear to be affected more than females.

Malignant melanomas look like raised lumps, often ulcerated, and can also look like gray or pink lumps in the mouth. Nail bed malignant melanomas, on the other hand, show up as toe swelling and possibly even loss of the toenail itself and destruction of underlying bone. Nail bed and footbed tumors often develop a secondary infection, leading to a misdiagnosis. These types of tumors usually metastasize to other parts of the body, decreasing the chances for a good outcome.

Mast Cell Tumors

Mast cell tumors are the most common types of skin cancer tumors. Mast cells release histamine, which is the chemical that causes some of the symptoms of allergic reactions in dogs, like irritation and itching. Mast cell tumors are cancer of these cells, and they can grow anywhere on your dogs skin, as well as in internal organs. The most common sites for mast cell tumors are the limbs, lower abdomen, and chest. About of mast cell tumors are found on dogs limbs.

Boxers, Pugs, Rhodesian Ridgebacks, Boston Terriers and older mixed breed dogs seem particularly susceptible to mast cell tumors, which most commonly affect dogs ages 8-to-10 years old. This cancer can be difficult to deal with, and your dog could have symptoms associated with toxins released from malignant mast cells, such as stomach ulcers, resulting from histamine release.

Squamous Cell Carcinoma

Skin squamous cell carcinoma is the most commonly diagnosed carcinoma of the skin, and primarily affects older dogs, especially Bloodhounds, Basset Hounds, and Standard Poodles. These tumors typically show up on the head, lower legs, rear, and abdomen, and appear as raised patches or lumps that are firm to the touch.

Exposure to the sun can be a cause of squamous cell carcinoma, but according to the National Canine Cancer Foundation, In dogs, the theory of exposure to sun is less obvious. It is believed that there may be some association with papilloma virus.

These tumors usually appear on your dogs abdomen, which is the area least protected from the sun by hair.

Histiocytic Cell Tumors

Histiocytic cells are a type of skin cell. When these cells proliferate into tumors, they are classified as histiocytic cell tumors.

These types of tumors are relatively common and typically affect dogs under 3 years old, especially Scottish Terriers, Bulldogs, Greyhounds, Boxers, Boston Terriers, and Chinese Shar-Pei.

There are three types of histiocytic cell tumors: histiocytomas, which are the most common; systemic histiocytosis, which mainly affects Bernese Mountain Dogs; and malignant histiocytosis, which also mainly affects Bernese Mountain Dogs and first shows up in the internal organs.

Fibrosarcoma

Fibrosarcoma and spindle cell tumors originate in the connective tissues of the skin and beneath the skin. These tumors can have a varied appearance, and while they are typically slow growing, they do tend to recur after surgical removal. Luckily, this type of tumor rarely metastasizes.

Fibrosarcoma usually affects dogs when they are middle-aged or older, with an average age of 10 years. Sometimes, an aggressive type of fibrosarcoma can affect young dogs. Your veterinarian will send off a sample of the tumor to a pathologist to determine whether or not the tumor is a low- or high-grade tumor, a classification that refers to the rate of cell division. This will help them give your dog an accurate prognosis and determine the best course of treatment.

This type of tumor is often found on the limbs. In addition to invading nearby structures, sometimes impeding their function, the tumors can also bleed, ulcerate, and become infected.

Symptoms of Skin Cancer in Dogs

The symptoms of skin cancer vary depending on the cancer, but in general, the best thing you can do to catch skin cancer early is to keep an eye on any strange lumps or bumps on your dogs body, especially as he ages.

Not all skin tumors are cancerous, and some, like skin tags, are usually benign sebaceous cysts or lipomas. However, if you discover an unusual lump or area of discoloration, play it safe and contact your veterinarian. Changes in the size, shape, color or ulceration of any growth or lump are also a cause for concern.

Diagnosing Skin Cancer in Dogs

Dog skin cancer is diagnosed by examining the cells of the skin tumor or lesion. Your veterinarian may perform a procedure called a fine needle aspiration, which takes a small sample of cells, or a biopsy, which removes a small portion of the tumor tissue or lesion by surgical incision. These samples are usually sent away to pathology for evaluation in order to obtain an accurate diagnosis.

Skin Cancer Treatment Options

A diagnosis of cancer for your dog is scary. Many types of skin cancer are treatable if caught early on, but it is understandable to feel worried.

Your dogs prognosis and treatment options will depend on a few factors, including the type of tumor, the location of the tumor, and the stage of the cancer.

Some skin tumors can be removed surgically to great effect. Others may require additional steps, such as radiation or chemotherapy.

Some types of cancer, for example malignant melanomas, are resistant to radiation therapy, while others, such as mast cell tumors, are more sensitive. Your veterinarian may refer you to a veterinarian oncologist when you have a cancer diagnosis. Veterinary oncologists have advanced training in cancer treatment.

Preventing Skin Cancer in Dogs

Some types of diseases are preventable, while others are not. As in humans, many cancers are the result of a genetic predisposition. In other cases, cancer is the result of a variety of factors coming together in an unlucky configuration, but there are a few things you can do to lower your dogs risk.

The risk factor most in your control is exposure to sunlight. If you have a light-skinned, short-haired dog breed, limiting your dogs exposure to direct sunlight, especially during the peak daylight hours, may help lower his risk of skin cancer.

The most important thing you can do to help your dog avoid skin cancer, however, is to familiarize yourself with all your dogs lumps, bumps, and rashes, perhaps during your daily grooming routine, and consult your veterinarian if you notice anything suspicious.

Melanoma

Overview

Melanoma

Melanoma is a kind of skin cancer that starts in the melanocytes. Melanocytes are cells that make the pigment that gives skin its color. The pigment is called melanin. This illustration shows melanoma cells extending from the surface of the skin into the deeper skin layers.

Melanoma is a kind of skin cancer that starts in the melanocytes. Melanocytes are cells that make the pigment that gives skin its color. The pigment is called melanin.

Melanoma typically starts on skin that's often exposed to the sun. This includes the skin on the arms, back, face and legs. Melanoma also can form in the eyes. Rarely, it can happen inside the body, such as in the nose or throat.

The exact cause of all melanomas isn't clear. Most melanomas are caused by exposure to ultraviolet light. Ultraviolet light, also called UV light, comes from sunlight or tanning lamps and beds. Limiting exposure to UV light can help reduce the risk of melanoma.

The risk of melanoma seems to be increasing in people under 40, especially women. Knowing the symptoms of skin cancer can help ensure that cancerous changes are detected and treated before the cancer has spread. Melanoma can be treated successfully if it is found early.

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Symptoms

Moles

Moles are usually harmless. They may contain hairs or become raised or wrinkled. Talk to your doctor about any change in the color or size of a mole or if itching, pain, bleeding or inflammation develops.

Melanoma

The first sign of melanoma is often a mole that changes size, shape or color. This melanoma shows color variations and an irregular border, both of which are melanoma warning signs.

The first melanoma signs and symptoms often are:

A change in an existing mole.
The development of a new pigmented or unusual-looking growth on the skin.

Melanoma doesn't always begin as a mole. It also can happen on otherwise healthy skin.

Melanomas symptoms can happen anywhere on the body. Melanomas most often develop in areas that have had exposure to the sun. This includes the arms, back, face and legs.

Melanomas also can happen in areas that aren't as exposed to the sun. This includes the soles of the feet, palms of the hands and fingernail beds. Melanoma also can happen inside the body. These hidden melanomas are more common in people with brown or Black skin.

Typical moles

Typical moles are generally a uniform color. They might look pink, tan, brown or black. In people with brown and Black skin, typical moles are more likely to be dark brown or black. Typical moles have a distinct border separating the mole from the surrounding skin. They're oval or round and usually smaller than 1/4 inch (about 6 millimeters) in diameter.

Most moles begin appearing in childhood and new moles may form until about age 40. By the time they are adults, most people have between 10 and 40 moles. Moles may change in appearance over time and some may even go away with age.

Signs that may indicate melanoma

Some moles aren't typical. They may have certain characteristics that indicate melanomas or other skin cancers. Characteristics may include:

Asymmetrical shape. Look for moles with unusual shapes, such as two very different-looking halves.
Changes in color. Look for growths that have many colors or unusual color patterns.
Changes in size. Look for new growth in a mole larger than 1/4 inch (about 6 millimeters).
Changes in symptoms. Look for changes in symptoms, such as new itchiness or bleeding.
Unusual border. Look for moles with unusual, notched or scalloped borders.

Moles that become cancers can all look very different. Some may show all of the changes listed above, while others may have only one or two unusual characteristics.

Hidden melanomas

Melanomas also can develop in areas of the body that have little or no exposure to the sun. These areas may include the spaces between the toes and on the palms, soles, scalp or genitals. These are sometimes referred to as hidden melanomas because they occur in places most people wouldn't think to check. When melanoma occurs in people with brown or Black skin, it's more likely to occur in a hidden area.

Hidden melanomas include:

Melanoma inside the body. Mucosal melanoma develops in the mucous membrane. This tissue lines the nose, mouth, esophagus, anus, urinary tract and vagina. Mucosal melanomas are especially difficult to detect because they can easily be mistaken for other far more common conditions.
Melanoma in the eye. Eye melanoma also is called ocular melanoma. It most often occurs in the layer of tissue beneath the white of the eye. This layer is called the uvea. An eye melanoma may cause vision changes and may be diagnosed during an eye exam.
Melanoma under a nail. Acral-lentiginous melanoma is a rare form of melanoma that can occur under a fingernail or toenail. It also can be found on the palms of the hands or the soles of the feet. Acral-lentiginous melanoma tends to be very dark, flat and have very unusual borders. It's more common in people of Asian descent and people with brown or Black skin.

When to see a doctor

Make an appointment with your doctor or other healthcare professional if you notice any skin changes that worry you.

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Causes

Where skin cancer develops

Skin cancer begins in the cells that make up the outer layer of the skin, called the epidermis. One type of skin cancer called basal cell carcinoma begins in the basal cells. Basal cells make skin cells that keep pushing older cells toward the surface. As new cells move up, they become squamous cells. Skin cancer that starts in the squamous cells is called squamous cell carcinoma of the skin. Melanoma, another type of skin cancer, comes from the pigment cells, called melanocytes.

Melanoma happens when something changes healthy melanocytes into cancer cells. Melanocytes are skin cells that make pigment that gives skin its color. The pigment is called melanin.

Melanoma starts when melanocytes develop changes in their DNA. A cell's DNA holds the instructions that tell a cell what to do. In healthy cells, DNA gives instructions to grow and multiply at a set rate. The instructions tell the cells to die at a set time. In cancer cells, the DNA changes give different instructions. The changes tell the cancer cells to make many more cells quickly. Cancer cells can keep living when healthy cells would die. This causes too many cells.

The cancer cells might form a mass called a tumor. The tumor can grow to invade and destroy healthy body tissue. In time, cancer cells can break away and spread to other parts of the body. When cancer spreads, it's called metastatic cancer.

It isn't clear what changes the DNA in skin cells and how it leads to melanoma. It's likely a combination of factors, including environmental and genetic factors. Still, healthcare professionals believe exposure to ultraviolet light is the leading cause of melanoma. Ultraviolet light, also called UV light, comes from the sun and from tanning lamps and beds.

UV light doesn't cause all melanomas, especially those that occur in places on your body that don't receive exposure to sunlight. This means that other factors may contribute to your risk of melanoma.

Risk factors

Factors that may increase the risk of melanoma include:

A family history of melanoma. If a close relative has had melanoma, you have a greater chance of developing a melanoma, too. Close relatives may include a parent, child or sibling.
A history of sunburn. One or more severe, blistering sunburns can increase your risk of melanoma.
Exposure to UV light. The ultraviolet light, also called UV light, that comes from the sun and from tanning lights and beds increases the risk of skin cancer, including melanoma.
Having many moles or moles that aren't typical. Having more than 50 typical moles on your body indicates an increased risk of melanoma. Also, having a type of mole that isn't typical increases the risk of melanoma. Known medically as dysplastic nevi, these moles tend to be larger than typical moles. They may have unusual borders and a mixture of colors.
Living closer to the equator or at a higher elevation. People living closer to the earth's equator experience more direct sun rays. Therefore, they experience higher amounts of UV light from the sun than people living farther north or south. Also, people who live at a higher elevation are more exposed to UV light.
Skin that sunburns easily. Anyone can get melanoma, but it's most common in people with white skin. If you have blond or red hair, light-colored eyes, and freckle or sunburn easily, you're more likely to develop melanoma.
Weakened immune system. If the body's germ-fighting immune system is weakened by medications or illness, there might be a higher risk of melanoma and other skin cancers. People with a weakened immune system include those taking medicines to control the immune system, such as after an organ transplant. Certain medical conditions, such as infection with HIV, can weaken the immune system.

Prevention

You can reduce your risk of melanoma and other types of skin cancer if you:

Avoid tanning lamps and beds. Tanning lamps and beds give off ultraviolet light, also called UV light. Exposure to this kind of light can increase your risk of skin cancer.
Avoid the sun during the middle of the day. For many people in North America, the sun's rays are strongest between about 10 a.m. and 4 p.m. Schedule outdoor activities for other times of the day, even in winter or when the sky is cloudy.
Become familiar with your skin so that you'll notice changes. Check your skin often for new skin growths. Look for changes in existing moles, freckles, bumps and birthmarks. With the help of mirrors, check your face, neck, ears and scalp.
Look at your chest and trunk and the tops and undersides of your arms and hands. Check both the front and back of your legs and your feet, including the soles and the spaces between your toes. Also check your genital area and between your buttocks.
Wear protective clothing. When you go outside during the day, wear clothes that help protect your skin from the sun's rays. Cover your skin with dark, tightly woven clothing that covers your arms and legs. Wear a broad-brimmed hat, which provides more protection than does a baseball cap or visor. Some companies also sell protective clothing. A dermatologist can recommend an appropriate brand.
Don't forget sunglasses. Look for those that block both types of UV light that come from the sun, called UVA and UVB.
Wear sunscreen year-round. Use a broad-spectrum sunscreen with an SPF of at least 30, even on cloudy days. Apply sunscreen generously. Reapply every two hours, or more often if you're swimming or sweating.