Skin Cancer in Dogs and Cats

Dr. Jacqueline Brister

Yellow Lab with a Skin Tumor

Skin cancer is a common cause for concern in dogs and cats, but it can be difficult for a pet owner to know what skin cancer looks like. Most types of skin cancer start as a mass or tumor on the skin. Some tumors are benign, or noncancerous, while others are malignant and more serious, leading to metastatic cancer, or the spread of cancer to other parts of the body. Listed below are common skin tumors seen in dogs and cats. Your veterinarian will be able to help you determine what type of tumor is present on your pet and what to do about it.

Lipoma

Lipomas are benign, or noncancerous, fatty tumors found in dogs and cats. They usually feel like circular, squishy lumps just beneath your pet’s skin. They typically grow slowly, but can get quite large over time. Treatment usually involves surgical removal. Surgery is generally not necessary unless the lipoma is in an area that will cause difficulty moving around (such as the armpit) or discomfort (such as a lipoma in an area that makes it difficult for the pet to lay down). Lipomas are more common in dogs.

Soft Tissue Sarcomas

These types of tumors typically lie on top of or just below the skin. They vary in size and shape, so they may be difficult to diagnose without a biopsy. While most don’t metastasize or spread to other parts of the body, they may grow rapidly and cause damage to the surrounding organs and tissues. Surgery may cure this type of cancer, but radiation is sometimes used when the tumor can’t be fully removed or if it comes back after it has been removed.

Mast Cell Tumors

These types of tumors can also grow just below or on top of the skin and will vary in size and shape. Mast cell tumors have the potential to metastasize to other parts of the body. They may also release chemicals that mimic an allergic reaction in your pet. Surgery can cure this type of cancer in mild cases. If the tumor cannot be fully removed or if the type of mast cell tumor is more severe, chemotherapy may be needed. Mast cell tumors are typically smaller and less severe in cats than in dogs.

Histiocytoma

This type of tumor is usually found on top of the skin, is pink and hairless, and may develop quickly. The good news with this type of tumor is that it will likely go away on its own! Unfortunately, it may look similar to cancerous masses such as sarcomas or mast cell tumors, and may need to be removed in order to discover what type of tumor it is. Histiocytomas do not occur in cats.

Squamous Cell Carcinoma

This type of tumor is cancerous and occasionally metastasizes. It usually feels like a hard lump just below the skin or is ulcerated and looks like a sore or an open wound. Squamous cell carcinoma can damage the nearby cells and tissues, but generally doesn’t spread quickly. The tumor also tends to bleed easily. Sun exposure is a common cause for this form of cancer. Surgery may cure this type of cancer in dogs but additional radiation and chemotherapy may be needed in cats.

Melanoma

This is a cancerous tumor that may be raised or flat and is often darkly colored. It may be found on any part of the body, including in the mouth. Many skin melanomas are benign, but some forms such as those found in the mouth or on the toes can be metastatic and spread to other areas of the body. Surgery may not cure the metastatic form but can help with the discomfort associated with the tumor. A vaccine is available but is not widely used and has certain requirements in order for it to work properly. The vaccine does not prevent melanoma. Melanoma of the skin is uncommon in cats.

Sebaceous Cysts and Sebaceous Gland Tumors

These cysts and tumors look similar and may appear as lumps just beneath the skin. Cysts are benign but sebaceous gland tumors can be benign or metastasize. Surgery will cure cysts or benign tumors, but may not fully cure malignant or metastatic sebaceous gland tumors.

Basal Cell Tumors

Basal cell tumors may also be called trichoblastomas. This type of tumor is benign and often appears as a small, circular tumor on the skin. Surgical removal will cure this tumor. This type of tumor is seen more commonly in cats. Basal cell carcinoma, a similar tumor in appearance, is cancerous and affects surrounding cells and tissues and may also metastasize.

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